1942: Geology

As has been the case in virtually every field of scientific endeavor, the effect of the war upon Geology has been profound. During the year 1942 the geological profession found itself confronted with the gigantic problem of conversion from a highly individualistic group concerned largely with the free inquiry into nature to a smooth-running machine closely integrated with the war effort. Emerging from the Golden Age of pure research that reached its crest in the 1920's with the American Museum of Natural History's Gobi Expeditions and other such elaborate undertakings, the profession has suddenly focused its attention upon the economic and military applications of its science.

This shift has caused important repercussions within the geological sphere. Some of the country's leading research institutions have found it necessary to curtail their usual activities, reduce their scientific staffs, and discontinue funds financing non-essential work. Science for science's sake has indeed become science for the nation's sake.

The petroleum industry, bereft of many of its geologists now engaged in government work, is experiencing a rapid decline in the production of oil, a great restriction of the exploratory work necessary in the search for new fields, and the continuous tapping of its reserves as the result of ever-increasing war demands.

The task of gearing this ramified science with our nation's 'All Out' effort has fallen to the National Roster of Scientific and Specialized Personnel of the National Resources Planning Board and the U. S. Civil Service Commission. In its capacity as the principal contact between the United States Government and the geological profession the Roster has made a tabulation of the nation's geological man-power, through the agency of the Geological Society of America, the Association of American Petroleum Geologists, and the American Institute of Mining and Metallurgical Engineers. The Geological Society of America's Committee on War Effort and similar bodies in other organizations have been designed expressly for this job of contacting the entire field by means of questionnaires, and for formulating plans for its utilization in the present emergency.

Formed in the last war for just such an exigency as this, the National Research Council is once more performing the duties for which it was originally intended.

This is primarily a war for land — land that will provide the wherewithal for the fabrication and powering of military machines. Both in the quest for vital minerals and fuels and their subsequent employment on the field of battle, the geologist is an all-important factor.

The steadily rising demand for war minerals, the exhaustive drain on already developed deposits, plus the loss of many sources of supply, have made the discovery of new ore deposits imperative. Hence the call for geologists, particularly those with experience in Latin American countries.

Rising to the occasion, the U. S. Geological Survey has trebled its staff. In cooperation with the United States Bureau of Mines, with State Geological Surveys, with the Mineral Advisor to the Materials Division of the War Production Board, with groups affiliated with the State Department, its members are conducting intensive investigations for strategic minerals both at home and abroad, especially in South America.

Recently several million tons of tungsten ore (that hardest of all metals so necessary in the manufacture of armor-piercing shells, gun breeches and bores) were added to our coffers through the enterprise of the Government Survey. From Idaho which bids fair to become a heavy tungsten producer, to Bolivia, our chief source of supply, American geologists are leaving no stone unturned in their quest for new mineral deposits. Hand in hand with the search for tungsten has gone the hunt for its principal substitute — molybdenum.

Mexico, where Dr. Paul Bateman of Yale has carried on such important work during the year, has been the scene of much field activity. Here mercury deposits, so valuable because of the acute shortage of this mineral, have been under the scrutiny of David Gallagher for the Metals and Minerals Division of the U. S. Geological Survey.

In the Argentine, J. T. Singewald of Johns Hopkins University has been studying the expansion of tungsten, mica and beryl production while his colleagues, William Buras and Quentin Singewald, have been conducting investigations in Columbia.

Quartz, greatly in demand because of the need for the quartz crystal oscillators used in radio transmission, is being sought eagerly in Brazil from which country, but a short time ago, it was shipped to the United States by plane.

Some Latin American countries have employed our men directly for the solution of their more pressing geologic problems. Such is the case of Norman D. Newell, former editor of the Journal of Paleontology and a member of the Geological faculty of the University of Wisconsin, who is now engaged in making a general stratigraphic survey of the Peruvian government's oil properties in the eastern part of that country.

Africa, too, has become an important base for the supply of raw materials to the United Nations. Here Dean Frasche is combing the Congo and the West Coast for tin, chrome, and tantalum while Anton Gray is subjecting Northern Rhodesia and other parts of the interior to intensive investigation.

In all this work the geologist is not only serving the purpose of uncovering new stores of ore, but is functioning as an American ambassador of good will continually striving to strengthen our Good Neighbor Policy and stimulate trade relations.

Aside from actual prospecting in the field, many members of the profession are occupying key positions on various executive and advisory boards in Washington, D. C. Outstanding in this group of men are Professor C. K. Leith, now the Government's chief authority on war minerals; Dr. Paul Bateman, chief of the Mineral Division of the Board of Economic Warfare in which body many of his fellow geologists are now serving; and Roy E. Dickerson whose intimate knowledge of Pan-America gained as a geologist for the Atlantic Refining Company is today being used to further our common cause.

Although the search for strategic metals is perhaps the geologist's primary function in war time, his activities in other phases less apparent, are of vital concern.

Engineering Geology's contribution in the construction of the vast system of hydro-electric units that power our war plants throughout the nation may escape the itinerant observer's attention. Nevertheless, since the St. Francis Dam disaster of 1927, this branch of Earth Science has played a notable role in the planning and erection of these huge public works. The most noteworthy achievements of the U. S. Bureau of Reclamation — Boulder Dam on the Colorado River and Grand Coulee on the Columbia, as well as the Tennessee Valley Authority's famous series of structures — were all made possible only through the perfect coordination of engineer with geologist.

Professor Charles Berkey of Columbia University has served the nation well and the world at large in this field of the Multiple-Purpose-Projects whose aim is flood-control, water conservation, and most significant, power for the wheels of industry.

In the stupendous war building program, concrete has assumed a new importance. Along with the accelerated construction of airdromes, barracks, fortifications, gun-emplacements, etc., has arisen the need for a particular type of fast concrete that will withstand repeated shock. Since the strength of this substance is determined largely by the elements used in its composition, it is readily seen that here is work for the petrologist. Research toward the development of better concrete has been given great impetus through the efforts of the Association of Cement Manufacturers, and the Bureau of Standards in Washington, not to mention the U. S. Bureau of Reclamation whose laboratory in Denver is thoroughly pursuing the petrographic study of this problem.

Militarily, the geological profession represents a vast reservoir of technical information that could well be used by our military leaders in the prosecution of the war. Though some progress has been made toward this end, the utilization of geology in a military sense leaves much to be desired.

The very nature of this war demands a deep understanding of the surface features of the earth. Where battle lines are in a continual state of flux over vast areas, the planning of campaigns, the establishment of operating bases, and the maintenance of troops necessitates a ready knowledge of terrain.

The geologist as a fighting factor has gained recognition slowly. Principally through the efforts, during World War I, of Colonel Alfred H. Brooks of the U. S. Army Engineering Corp and the U. S. Geological Survey, the military mind has been led to accept geology as an important adjunct to the Armed Services. As Chief Geologist with the A.E.F. attached to General Headquarters, he organized a geological staff that rendered the Allies invaluable service during the conflict of 1917 and 1918. Today his report on The Use of Geology on the Western Front is being used as an indispensable handbook by the fighting geologists of 1942.

The army that can turn the very rocks upon which they fight into their allies is doubly assured of victory. With this in mind a corps of 'Terrain Analysts' composed of geologists drawn from various branches of the Armed Forces has been organized to act in conjunction with Armored Tank Divisions during actual operations. A training program to acquaint these men with their special duties at the front is now being carried out at the Armored Force Headquarters at Fort Knox, Kentucky. This small group will undoubtedly form the nucleus for other similar units that will be developed elsewhere.

Toward the solution of problems revolving around the ground-water supply for troops in the various theatres of war, a special division of the U. S. Geological Survey acting as a liaison between the geological profession and the General Staff and also in the capacity of an advisory board to our military leaders, has taken up the work of supplying the Service with geological maps of the fighting fronts.

In the field of active operations the cooperation of the army engineer with the geologist is essential in the sinking of underground ammunition dumps, hangers, bomb-shelters; in camouflaging strategic points; in the selection of suitable rock formations as foundations for heavy artillery emplacements; in the construction of earthworks with their network of intercommunicating trenches; in the utilization of natural obstacles toward offence or defence; in determining strategic locations for the erection of airdromes; in the location of water-bearing strata for the establishment of an army's water supply; in the location of campsites with good drainage conditions for the installation of latrines, cesspits, and germicidal plants; in advising on the placement of land-mines and tank traps; and the composition of surface mantle (rocks, soil, sand) that will affect the maneuverability of tanks and other motorized vehicles.

The strategist draws heavily upon his knowledge of the physical character of the land over which a contemplated advance is to be made. Avenues of attack, natural strong points upon which to concentrate, spots in which to regroup or retrench are all greatly influenced by the advice of the geologist. His acquaintance with topography and map reading is utilized by the Air Corps in interpreting aerial photographs of enemy territory.

In the development of landing techniques to be used by invasion forces, work has been going along steadily on our west coast where Francis Shepard is making a special study of beaches and shorelines. It is said that the astounding success of the landing operations on the coast of Morocco and the initial advance of American troops into Tunisia was in part due to expert geological work of this nature.

War, destructive as it may be, stimulates enterprise in geology as in every other field of endeavor. In this struggle new applications will be found for the Earth Science, new horizons for the geologist to conquer. So it was in the last war when Max Mason and L. B. Schlichter, based on ideas taken from their war experience of 1917-18, organized the first Geophysical Prospecting Company and started Geophysics off on its great mission of usefulness to mankind.

1941: Geology

Geologic studies in North America during 1941 do not show a marked impress of world war conditions in so far as can be discerned in published reports. Current work of many organizations and individuals, however, is largely directed to study of 'strategic minerals,' such as those containing commercially important content of manganese, chromium, aluminum, magnesium and mercury. These are especially needed in America's war efforts. Also, there are many other geologic subjects of practical importance at the present time, such as those related to military and engineering work, and water supply. This work is being done chiefly by governmental surveys. The scientific staffs of some of the surveys have been expanded notably and geologists are now being employed by the U.S. Army, the U.S. Department of Agriculture and other bureaus.

One result of the war is the almost complete curtailment of scientific intercommunication between the United States or Canada and other lands, at least those outside of the Western Hemisphere. Worthy of special comment, also, is the role of mineral deposits in various parts of the world as objectives of military strategy. This includes the coal and iron deposits of the Donetz Basin in southern Russia, the petroleum fields of the Caucasus and Iran, the great tin deposits in Malaya, and the petroleum and other minerals of the East Indies. Mineral wealth, which is basic to modern industry, is increasingly a factor in world economics and polities.

Fundamental Problems.

Sponsored by a committee of the National Research Council and supported by liberal research grants from the Penrose fund of the Geological Society of America, an active research program on problems of the radioactivity of rocks and on age determinations of rocks as measured by accumulated radioactive disintegration products has been carried on since 1930. Reports of this work published in 1941 give revised average values for the radioactivity of several important types of rocks. The new measurements indicate that the rate of generation of radioactive heat within the earth is substantially less than had previously been supposed. This has significant bearing on various hypotheses of vulcanism and mountain building. One of the most interesting and promising results of radioactive studies of recent date has been improvement of techniques in measurement of geologic time by analyses of the helium content of rocks. Results that accord well with measurements of the uranium-lead ratios indicate reliability of the age computations based on helium determinations. This is significant because studies using the helium method are applicable to many more types of rock than those based on the uranium-lead ratio.

Earth Structure.

Problems of mountain building have been under special investigation for several years in a part of the Rocky Mountain system centering in northwestern Wyoming. A most recently published report by M. Demorest (Yale University) summarizes evidence found in the Big Horn Mountains which indicates a primary deformation at the close of Cretaceous time that produced a great asymmetrical upfold of the earth's crust and a distinctly later secondary episode marked by thrust faults. Gravel deposits were formed between the times of these movements.

Recent studies reported by Gutenberg (California Institute of Technology) report that mean sea level is rising at an average rate of about 10 cm. per century. Parts of continental masses, especially in northern North America, and northeastern Europe, are rising differentially because of the unloading due to melting of glacial ice caps. The maximum observed present rate of land uplift is in the region of Hudson Bay, where uplift is determined to be two meters per century. These changes in sea level and uplift of continental masses are correlated with plastic movements of the crustal zone, which on seismic data is computed to be about 70 km. thick. Some deep focus earthquakes, originating at depths up to 700 km. are seemingly associated with these crustal changes and indicated deep-seated slow movements of earth materials.

Seismology.

An important special publication of the Geological Society of America, 'Seismicity of the Earth' by Gutenberg and Richter gives data both on deep focus and shallow earthquakes, including 54 great shocks between 1904 and 1939. The earth's surface is shown to consist of relatively inactive blocks that are separated by active zones. The latter include a circum-Pacific belt, a Mediteranean-Trans-Asiatic trend, and a few narrow belts of localized shallow shocks. The circum-Pacific zone includes all of the very deep shocks and a large majority of the shallow ones. Most of the Pacific basin and the continental areas are relatively inactive, but small shocks may occur everywhere. (See also SEISMOLOGY.)

Oceanography.

First detailed description of the submarine topography off the California coast is contained in a 'Special Paper of the Geological Society of America' by Shepard and Emery published in 1941. Maps showing configuration of the earth's floor are based on 1,342,000 soundings, some reaching to depths of more than 13,000 feet below the sea level. Submerged topographic forms include steep-sided peaks, plateau-like areas, prominent escarpments, flat-bottomed basins, and very deep V-shaped canyons. The problem of the origin and history of the canyons is treated at length. It is believed that the canyons were formed during the last 100,000 years, but no single process that has been suggested is thought adequate to explain these canyons. The authors think that most of the erosion was accomplished by running water above sea level, but they admit the extreme improbability of the changes of sea level amounting to several thousand feet that are required by this hypothesis. The explanation of the submarine canyons that has been offered by R. A. Daly (Harvard University), which ascribes the erosion to work of turbidity currents on the sea floor, is now supported by laboratory observations and seems most satisfactorily to account for these perplexing features of the continental shelves. Seemingly they were formed during Pleistocene time when sea level was lowered a few hundred feet by removal of water to make continental ice caps.

Core samples of sea-bottom sediments, some nearly 17 feet in length and obtained from depths up to 16,000 feet below sea level, are now supplying new evidence concerning conditions of sedimentation in the ocean basins. A recent study of such cores from the Bartlett Trough south of Cuba (J. A. Cushman, American Journal of Science) shows successive warm and cold water assemblages of foraminiferal shells and permits correlation of the zones that are recognized in different cores taken some hundreds of miles apart.

Glacial Geology.

The project to compile a detailed glacial map of North America, formulated by a committee of the National Research Council, has served in recent years greatly to stimulate studies of this branch of Geology. A number of special projects have been supported by grants from the Penrose fund of the Geological Society of America. There is now general agreement as to classification of the major divisions of the Pleistocene deposits and, under chairmanship of R. F. Flint (Yale University), materials for the new map are nearing completion. Correlative studies of much interest relate to marine terraces along the Atlantic and Gulf seaboards and these have been the subject of recently published papers. Two well-recognized old shore lines, 25 and 100 feet respectively above present sea level, are recognized and additional ones up to 270 feet elevation are determined less definitely. These shore lines are associated with changes of sea level at times of glaciation and reglaciation.

Economic Geology.

Estimated petroleum reserves of North America at the present time amount to about 18,000,000,000 barrels. Work by petroleum geologists is needed continually to replenish these reserves as oil is consumed. Present trends in this field of work emphasize use of the microscope and detailed stratigraphic subsurface data, leading to better understanding of the conditions and places of oil accumulation. A growing number of petroleum geologists is being drafted for executive and managerial positions in the industry.

Many publications on the geologic problems of metalliferous deposits and of nonmetallic resources are found in the literature of 1941. These are most conveniently summarized in the 'Annolated Bibliography of Economic Geology' (Urbana, Ill.) which is available in most scientific libraries.

Continued application and improvement of geophysical methods in explorations for many types of useful earth materials may be reported. Two important books on this subject were published in 1940 (Jakosky, Heiland). An interesting current investigation is the application of several different techniques to measurement of anomalies caused by a single ore body; this work, which is being done in the Tri-State lead and zinc district of Kansas-Oklahoma-Missouri, indicates the value of independently derived geophysical and geological data.

Paleontology.

Numerous papers describing new species of fossil plants, invertebrates and vertebrate fossils, totaling thousands of pages and hundreds of plates, are contained in publications of 1941. Many of these are very important but they are highly technical. Most are contained in the Journal of Paleontology (Tulsa), the Geological Society of America, and reports of Federal and state surveys. An especially noteworthy publication is L. W. Stephenson's monograph on 'Late Cretaceous Fossils of Texas' published by the University of Texas. (See also PALEONTOLOGY, VERTEBRATE.)

Stratigraphy.

A considerable number of geological papers published annually deal with description of the stratified rocks of various regions, their economic resources, and the geologic history that they represent. These are too varied and mostly too technical for special notice. Worthy of record, however, is the establishment in 1941 of a commission representing all of the major geological societies and surveys in North America to deal with general questions of classification and nomenclature of rock units.

An important contribution to knowledge of the continental Tertiary deposits of North America is contained in a collaborative report by H. E. Wood and a group of workers (Bulletin Geological Society of America) in which seventeen faunal zones are recognized. Each zone is named from a characteristic genus of extinct mammal. An elaborate correlation chart shows the distribution of the deposits throughout North America and local formation names.

One of the most important and interesting aspects of studies in Historical Geology is the variation in types of sediments deposited from place to place during a given epoch of geologic time. This variation in the nature of the deposits is designated as facies. An illuminating discussion of the problems of facies is given by C. O. Dunbar (Bulletin Geological Society of America) in his presidential address before the Paleontological Society. This deals with characters of the Permian rocks and fossils in several parts of the world.

1940: Geology

Impact of the European War II is an outstanding feature in the record of geological studies and activities in 1940, but effects of the conflict on three continents cannot be gauged fully. Scientific activities of the warring countries are either modified for war ends or have been very greatly curtailed, in part through transfer of personnel to strictly military activities.

Mineral Deposits.

In the field of geology intensive work has naturally been turned to investigation of mineral deposits having important economic and military significance. Petroleum, coal, and other fuels, metals such as iron, copper, manganese, tin, tungsten, mercury, and many others, as well as nonmetallic substances of various sorts must be made available, and demands for some of them have been greatly increased. Impairment or stoppage of trade between countries, especially that involving transportation by sea, has imposed the necessity of finding and utilizing whatever sources of supply may be available to the various countries. Mineral deposits that are not exploitable under normal economic conditions may assume importance, and the geologist is called on to make studies of all such deposits. This is true also of the United States, where currently a large part of the activities of the U.S. Geological Survey, the Bureau of Mines, and of several state geological surveys is directed to investigation of so-called strategic minerals. Another important, but intrinsically less vital, aspect of the war situation has been the interruption of scientific communications. Accordingly, knowledge of the scope and results of recent geological studies in foreign countries is not at hand. Shipment of American publications to countries of the war zone also is withheld. The International Geological Congress, which was to have assembled in London during the summer of 1940, was cancelled.

A noteworthy contribution to the study of ore deposits, especially of the metals, is a treatise by L. C. Graton, Harvard University, on the nature of the ore-forming fluid (Economic Geology, 1940). The dominant factors in ore genesis are believed to be nature of the source (generally molten igneous material), a means of independent separation, and a motive power of ascent for hot alkaline liquid extracted from magma at a late stage in cooling. Attention is directed to the profound contrast between the normal confined conditions of depth where ore concentrations are generated, and near surface conditions where many ore metals are deposited. Gaseous emanations from magma are held to be of small importance as agents of transportation or deposition of minerals, and it is believed that petrologists have overemphasized the importance of magmatic gases in the differentiation of igneous rock types and in other chemical changes. (See also MINERALOGY.)

Lead and Zinc.

A collaborative study of the lead and zinc deposits of the Mississippi Valley region, edited by E. S. Bastin (Geological Society America, 1940), is an interesting recent contribution to economic geology. That the ores of this area, which contains the greatest lead-and-zinc-producing districts in the world, were borne by ascending hot waters from igneous sources is a somewhat surprising conclusion in view of the almost complete absence of known igneous rocks in this region. Disagreement as to origin of the ores remains because some geologists assert strongly that evidences favor a cold water origin by leaching and redeposition of the mineral matter.

Phosphates.

Recent studies of phosphate deposits of the United States (G. R. Mansfield, in Economic Geology, 1940) indicate that the known reserves of Florida and Tennessee, chief producers in Eastern United States, are much larger than previously estimated. Estimates of reserves in Western states are increased somewhat, and the total for the United States is considered to exceed 10,000,000,000 tons, which at present rate of annual consumption is sufficient for more than 3,000 years.

A second edition of W. H. Emmons 'Principles of Economic Geology' indicates the tremendous progress that has been made in this field since the publication of the first edition, twenty-three years earlier. The book contains excellent concise descriptions of the principal types of ore deposits and summaries of the geology of leading producing districts, both within and outside the United States. Discriminating choice of material, including illustrations, and avoidance of useless details, contribute much to the value of the book. (See also MINERALOGY).

Physiography.

A comprehensive and authoritative work of general scope is the 'Geology of North America,' edited by R. Ruedemann and R. Balk. The first volume, which is all that has yet appeared, contains 16 contributions by American geologists dealing with introductory material and the geology of the stable areas of the continent. It is unfortunate that war conditions very probably will interfere with the issue of the remainder of the work. Attention may be called also to W. W. Atwood's 'Physiographic Provinces of North America', which contains numerous and exceptionally fine illustrations of typical land forms in all major subdivisions of the continent, accompanied by descriptions that are adapted for the general, non-technically trained reader. A noteworthy feature of the book is a large physiographic diagram of the United States by E. Raisz. This map is geographically the most accurate and artistically the best rendered of any such map that has appeared.

Volcanoes.

T. A. Jaggar, famed volcanologist, who for many years has studied eruptions of lava in Hawaii and other parts of the world, has recently published a summary of his study on volcanic gases (Am. Jour. Science, May 1940). Collection of gases coming from molten magma at a temperature of 1,000° to 1,200° C. involved numerous hazards and called for special technique. Jaggar's studies have shown that carbon dioxide, nitrogen, water, sulphur trioxide, hydrogen, and other gases are important constituents of volcanic emanations, their proportions varying under different conditions, especially where atmospheric admixture and combustion is possible. Chemical reactions are in general strongly heat-producing. These studies throw light on characters of igneous rocks and they bear both on an understanding of the mechanism of various types of igneous intrusion and eruption and on possible conditions of the earth depths where magmatic conditions and seismic activity are important. (See also SEISMOLOGY.)

Sedimentary Deposits.

A new book by W. H. Twenhofel, 'Principles of Sedimentation,' has special value in many geologic studies. The volume emphasizes the concept that the nature of any sedimentary deposit is determined less by its sources than by the environment under which it was produced, transported and deposited. It is shown that fossils in some sedimentary rocks have been transported after death to be buried in an environment quite different from that under which they lived and died. Bottom-dwelling animals on muddy sea floors devour the mud in order to extract organic matter from it, as shown by studies of modern lobworms, indicating that the entire bottom sediments to a depth of nearly two feet passed through the bodies of these creatures in a period of about 22 months. Another valuable work in this field is a volume ('Recent Marine Sediments'; Am. Assoc. Petroleum Geologists, Tulsa, Okla.) prepared by the Committee on Sedimentation of the National Research Council, P. D. Trask, Editor. Its 34 separate papers offer much important new information on various aspects of marine sedimentation.

Submarine Canyons.

One of the most puzzling geologic problems that in recent years has specially engaged the attention of several American investigators is the origin of the deep submarine canyons that intersect the eastern and western continental shelves of North America and that are known also in some other parts of the world. A scholarly book, 'Origin of Submarine Canyons' by Douglas Johnson, Columbia University, offers a critical review of the hypotheses that have been advanced, including one proposed by the author suggesting that a dominant factor in making these canyons is the solvent action of seaward movement of ground water from the land, forced by artesian pressure through shelf sediments and producing mud flows near their outer margin.

Ice, Hardness and Erosive Power.

Hardness is a relatively constant property of most mineral substances. According to Eliot Blackwelder of Stanford University, President of the Geological Society of America in 1940, ice is a mineral that ranges considerably in hardness according to temperature. This fact does not appear in textbooks of mineralogy and is overlooked by geologists who generally are well informed of the importance of glacial ice as a geologic agent of erosion and deposition. Near the freezing point ice has only the hardness of gypsum, and at this temperature a glacier erodes only because of hard rock held in its base or sides. At 50 to 60 degrees below zero Fahrenheit, ice has almost the hardness of feldspar and is more resistant than most common rocks. Such temperatures are by no means unknown in the coldest parts of the globe and here moving ice masses or particles blown by strong winds have distinct erosive power owing to increased hardness of the ice at very low temperatures.

Stratigraphy.

Stratigraphic studies on all parts of the geologic column and pertaining to many different areas have, as usual, large aggregate volume in publication. Special interest attaches to recent efforts toward clarification of the principles of classification and nomenclature of sedimentary rocks. A committee of the American Association of Petroleum Geologists has published (A. A. P. G. Bulletin, February 1940) recommendations on this subject in connection with a proposal to recognize certain standard divisions of the Permian system in North America, based on the section in western Texas. Among more important stratigraphic contributions of state geological surveys is a volume on the Devonian system in Pennsylvania (July, 1940). The report is important not only because this area contains one of the best developments of Devonian rocks on this continent, but because of numerous excellent illustrations of guide fossils and because of general application of its attack on problems of classifying formations of similar lithologic character but different age (facies distributing).

Classification and Nomenclature of the Organic World.

A paper that is important to paleontologists, as well as to zoologists and botanists who are concerned with classification and nomenclature of the organic world, is a discussion by G. G. Simpson (Am. Jour. Science, June, 1940), of fixed name-bearing functions of 'type specimens,' in contrast to a properly flexible group concept in definition of species, genera, and higher divisions. The collective term hypodigm, meaning examples, is proposed to include all accepted published representatives of a given classificatory assemblage, thus clarifying and simplifying taxonomic procedures.

Paleobotany.

The most up-to-date and generally useful treatise on fossil plants is a textbook of paleobotany by W. C. Darrah, Harvard University. Although intended as an introduction to the science, the reader is assumed to have knowledge of some botany and historical geology. The material is well organized and the book is well written.

1939: Geology

Noteworthy progress in geological studies is being made each year. This is due partly to the fact that the number of research workers in this field of science is constantly increasing, and partly to increased financial support both from governmental and private sources, the latter including numerous important commercial organizations and very many allotments from various research funds. Collectively, this reflects a growing recognition of the importance of geological studies.

Civilization and the politico-economic relations of peoples are basically influenced by the distribution and control of materials in the earth. Mineral resources furnish essential keys to progress in modern industrial development, and lack of such resources imposes well marked limitations on the status of certain nations as actual or potential world powers. The outbreak of European war in 1939 and the hostilities in the Far East are both traceable to a struggle between 'haves' and 'have-nots.' Great Britain and the United States together control about three-fourths of the world's supply of needful minerals. France and Russia hold the bulk of the remaining one-fourth. Germany lost 50 per cent of its annually needed supply of iron when Lorraine was ceded to France; cost of gasoline manufacture in Germany necessitates a price four times higher than the world market; this nation produces only 14 per cent of its required copper and lacks supplies of fifteen necessary industrial minerals.

New contributions to geologic knowledge that are of special importance or interest and that are representative of innumerable studies that cannot be reviewed, are noted according to divisions of geologic science.

Fundamental Problems.

Among the most important lines of research that bear on fundamental problems of geology are laboratory investigations of the chemical and physical character of rock substances especially under conditions of high temperatures and pressures such as exist at depths of some miles beneath the earth's surface. The most extensive and valuable work in this field has been carried on since 1907 by the Geophysical Laboratory of Carnegie Institution of Washington. In 1939 Publication 1999 of the Laboratory was issued, a 400-page contribution containing 23 research papers by members of the staff, and appropriately this was dedicated to the recently retired director of the Laboratory, Dr. Arthur L. Day, who had guided the program of investigations from its inception. With development of many special types of apparatus and previously untried techniques, a multitude of qualitative and quantitative data, especially concerning the nature of igneous rock magmas and the mode of origin of igneous minerals and rocks, has been added to knowledge. Magmas (including lava) are high temperature silicate solutions of complex character in which known physical and chemical laws operate to control crystallization and solidification.

Tests to determine the strength, compressibility, conductivity and other physical properties of many rock and metallic substances under extreme pressures have been in progress during recent years, especially in the laboratory of P. W. Bridgman at Harvard University. Pressures equal to those existing in the earth at depths of approximately 109 miles have been attained. Such studies are difficult and not without danger, since not a few tests have ended in explosions, but they are of utmost value not only in showing physical properties of matter but in guiding geologic interpretation of seismologic and other data that relate to conditions of the earth interior. Many fundamental problems of geology call for greater knowledge of the constitution and dynamic state of different depths beneath the earth's surface. Some of the laboratory investigations here noticed have undertaken to combine high temperature and high pressure, but much work that promises interesting results remains to be done. An additional factor to be investigated is the effect of time. Researches have just been reported on deformation produced in several minerals and rocks by relatively low but long-continued pressures. This study appears to establish both a type of elastic flow and a displacement that is termed pseudoviscous flow, and it is observed that conditions differ greatly in tests on dry and on water-saturated specimens.

The subject of mountain-building may be said to have engaged the special interest of practically all geologists during past and present time, although only a fraction of earth-scientists have been specially engaged in the effort to explain how mountains originate, why they undergo re-elevation after being worn down to a lowland, why recurrent epochs of mountain-making crustal deformations separated by long periods of crustal quiescence mark past earth history, and why mountain ranges of different geologic ages are located in certain belts. The subject of mountains is naturally of great interest also to very many who are not geologists. A new book ('Architecture of the Earth,' by R. A. Daly) that treats these matters in relatively simple manner and that brings together the most significant results of modern studies on the physical and dynamic characters of the earth's interior has been written by a leading American geologist and world authority. Also noteworthy is 'A Theory of Mountain-building' (David Griss, Am. Jour. Sci., 1939) which correlates in very interesting manner the numerous lines of pertinent evidences, such as occurrence of long narrow belts of abnormally low gravity paralleling recent mountain folds in the East and West Indies, coincidence of mountain belts with depressed sediment-filled troughs (geosynclines), and the record of vertical upwarping in re-establishing crustal equilibrium (isostasy). These, along with other elements of the problem, direct attention to the nature of sub-crustal forces, and convective heat transfers within the earth are concluded to exert chief control in the development and evolution of the crustal irregularities that make mountains.

Geomorphology.

Scientific studies of the nature, classification and nomenclature of surface features of the earth, and particularly inquiries as to the origin of these features, customarily have been grouped under the head of Physiography. A noteworthy tendency to replace the name of this time-honored branch of geology by the more dignified (?) title of Geomorphology is evident at the present time. In 1938 a new periodical called the Journal of Geomorphology was established under the very able editorial leadership of Prof. Douglas Johnson, Columbia University and an associated group of seventeen physiographers who are well distributed internationally. The eight numbers of this journal that have appeared contain an unusually interesting and scholarly series of papers, published in English, French and German. After a period of several years in which no books of any importance to geomorphology were issued, four very noteworthy works have appeared almost together. These are N. M. Fenneman's 'Physiography of Eastern United States' (1938), and textbooks of geomorphology by S. W. Wooldridge and R. S. Morgan (London, 1937), P. G. Worcester (1939) and A. K. Lobeck (1939). The book by Lobeck has been characterized by one reviewer as the most beautifully illustrated treatise in geologic literature.

Economic Geology.

During recent years considerable increase in studies devoted to chemical, physical and economic aspects of American coal deposits is observable, and the relation of determined features to geologic occurrence of the different types of coals has received attention. Coal is not simply a combustible substance that is preferable to firewood for making steam in a locomotive and for many other uses as an ordinary fuel. Even as fuel, one coal is by no means the same as another, and different parts of a single bed may be very dissimilar in properties. The Illinois Geological Survey, which in 1936 initiated a new program of intensive research on coal, has lately published reports showing various important determinations that bear on improved utilization. As a guide in geologic discrimination and exploration the Survey has found recognition of four ingredients in coal of practical value in description and classification. These substances, first identified in England, are coal-matter called vitrain, clarain, fussain and durain. In some cases, the segregation of these elements in mined coal is practicable and yields materials of very different suitability for technologic uses. Several hundred chemical compounds that are useful in industry are derived from coal. Another feature of interest in coal studies that is applied in Illinois and, according to recent publications from Holland and Poland, in some coal basins of Europe, is use of the various kinds of plant spores (reproductive elements more primitive than seeds) that are found in different coal beds for purposes of identification and correlation of the beds. A recent British book on coal (A. Rastrick and C. E. Marshall, 'The Nature and Origin of Coal and Coal Seams,' 1939) is the most outstanding publication now available on this subject.

Geologic investigation of oil and gas fields and exploration for new producing territory furnish employment to a much larger group of workers than any other branch of the science. The United States is much the largest producer and consumer of petroleum among the nations and although its present estimated reserve oil supply exceeds 15,000,000,000 barrels, activities in production and exploration have shown no decline. Only a small part of the potential yield of many fields is annually produced however. Geologic and geophysical work which was responsible for increase in oil production in Illinois, some 20,000,000 barrels annually, beginning in 1937, has been extended to the Forest City Basin in northeast Kansas, and adjoining parts of Nebraska, Iowa and Missouri; this has led to the first commercial production of oil in Nebraska.

Stratigraphy.

A considerable part of geologic literature deals with the description of correlation of sedimentary rocks and in some cases of associated other types of rocks. This field of study commonly involves problems in classification according to physical and paleontologic characters. Local and regional historical geology and interpretations of former geographic environments (paleogeography) are based mainly on stratigraphy.

A recent systematic study of Silurian formations in Ohio with quantitative determination of chemical characters, including especially insoluble constituents of individual layers has proved extremely useful in subdividing and tracing equivalent deposits. New exposures of Upper Ordovician and Lower Silurian formation in Pennsylvania indicate that the mountain-making crustal deformation called the Taconic orogeny is to be dated within the late Ordovician rather than at the close of this period (unless the accepted Ordovician-Silurian boundary is shifted downward). Recent very important studies of Mesozoic deposits in western Nevada reveal existence of Triassic and Jurassic zones not previously known to exist in North America; in a sequence of deposits that has maximum thickness of 30,000 feet, continuous sedimentation from Triassic into Jurassic time is evidenced, although elsewhere a noteworthy hiatus in the geologic record occurs at this horizon. Investigation of continental and marine Mesozoic beds in the Rocky Mountain region has served to clarify the relations of debated beds near the Jurassic-Cretaceous boundary and to indicate satisfactory definition of this datum.

Paleontology.

Two new books concerning fossil plants are welcome additions to the literature because they are well written treatises of general scope and because no similar works have appeared for many years. Prof. W. C. Darah of Harvard University is the author of both books ('Principles of Paleobotany,' 'Textbook of Paleobotany'). A beautifully published monograph on one of the oldest known groups of cone-bearing plants (Lebachia), of Carboniferous and Permian age, is the work of the Swedish paleobotanist, R. Florin. Recently discovered remains of the somewhat common but generally very poorly preserved Devonian woody plant called Callixylon, show it had curious pairs of laterally directed long spike-like leaves arranged at intervals along the stalk; the well preserved fossils on which these determinations were made come from Pennsylvania. Publications on the laminated calcareous fossil remains of primitive seaweeds (algae) from pre-Cambrian and lower Paleozoic formations indicate several distinguishable types that appear to have value in marking stratigraphic horizons.

Among many reports devoted to fossil invertebrates mention may be made of a monograph of outstanding importance that deals with the previously unknown brachiopod faunas of Late Cambrian and Early Ordovician age. This work, by E. O. Ulrich and G. A. Cooper, of the U. S. National Museum, furnishes information concerning the beginnings of brachiopod stocks that became dominant in various later Paleozoic faunas. A surprising discovery, of special interest to vertebrate paleontology, was the capture by a South African trawler of a large coelacanth fish, of a type not previously known to have survived beyond Mesozoic time. This fish was illustrated in an issue of Life (April 3, 1939).

An interesting study (by R. R. Shrock) on Silurian marine deposits of Wisconsin calls attention to certain peculiarities of the rocks that are associated with highly localized distribution of abundant fossils. This had been observed in other parts of the Mississippi Valley region but not previously investigated closely. Locally, within the otherwise evenly bedded strata, there are nearly structureless masses 10 to 50 feet or more in thickness and a few yards to a mile in diameter. Fossils are scanty in the well bedded layers, but are found to be extremely abundant in some of these local masses. There are indications that the fossiliferous areas stood as low mounds a few feet or tens of feet above the surrounding shallow sea bottom at the time these rocks were being formed, and thus they somewhat resemble coral reefs. Unlike the coral reefs, however, these Silurian deposits contain numerous other kinds of marine invertebrata, and also calcareous deposits made by seaweed (algae).

Oceanography.

Development of a new technique for securing cores from the sea bottom has yielded samples up to ten feet in thickness, some from depths as great as 12,000 feet. The microscopic shells of Foraminifera, obtained from different layers in the cores, prove existence of former cold water assemblages off the New England coast, above which there are warm water assemblages.

One of the subjects that at present holds greatest interest to all geologists is the problem of the origin of the numerous profound canyons that indent the eastern and western margins of the North American continental shelf and the submerged borders of other continents. Some of these canyons are more than 60 miles long, 2 miles wide at their lower end, and they descend to depths of as much as 10,000 feet below sea level. Douglas Johnson (1939) has reviewed critically the known data and various hypotheses of origin that have been advanced, and has ably marshalled evidence to support deductions as to the possible agency of water circulating through and squeezed out of sediments of the continental shelf in producing these amazing canyons.

Petrology.

A large number of reports describing the structural relationships, macroscopic and microscopic, textural character and chemical nature of igneous rocks are published each year, but greatly increased attention to investigation of sedimentary rocks is steadily modifying the emphasis in petrologic studies. Two new text books dealing with sediments are the work of an American (F. G. Tickell, 'Examination of Fragmental Rocks') and two British authors (F. H. Hatch and R. H. Rastall, 'Petrology of Sedimentary Rocks'). An extended utilization of study technique belonging to the so-called Sander method of petrofabric analysis is being employed in a variety of work on rocks. Study of the quartz grains in an average sandstone, for example, has recently indicated an average slight elongation of the rounded fragments that prove to be oriented in the direction of the optical axis of the mineral.

Seismology.

Further investigation of deep-focus earthquakes by B. Gutenberg and C. F. Richter (October 1939) has shown that when these are divided into groups with shocks originating respectively at depths of 50 to 300 kilometers, and at depths exceeding 300 kilometers, a well defined geographic separation is observable, especially on the borders of the Pacific Ocean where very numerous recent records have been secured. Both groups of foci are definitely related, however, to belts of geologically recent crustal deformation and vulcanicity. (See also SEISMOLOGY.)

Regional Geology.

A work of special interest to American geologists, and to all others who have need for an authoritative, full but concise summary of modern knowledge of the rock succession and geologic structure of North America, is publication in 1939 of a volume of 'Geologie der Erde' dealing with this continent. Although printed in Germany, the book is in English. It is the work of 16 American geologists who are severally responsible for treatment of assigned regions in which they have done extensive work. The last published similar publication, which was part of an international series, was a relatively brief treatise by a single author that appeared in 1912.

Recent History.

The Geological Society of America celebrated the fiftieth anniversary of its founding in meetings held at New York City in December, 1938. During 1939 the Society undertook publication of a special anniversary volume on the development of geology during the past half century. This treats some twenty divisions of geologic science in chapters prepared by specialists and is not confined to North America. Among American geologists of world renown who died in 1939 are Arthur P. Coleman, who made outstanding contributions to studies of glacial deposits, and George H. Girty, paleontologist, whose life was devoted to studies of Late Paleozoic invertebrate faunas.

1938: Geology

Estimates based on membership in American geological societies and available data from other continents indicate that more than 10,000 persons in different parts of the world are actively engaged in geologic work as a profession.

Many additional persons contribute directly or indirectly to advancement of geologic knowledge. The range of studies being carried on is certainly much wider than in any other field of science, for geology embraces application of all sciences to the enlargement of knowledge about the earth. Increasing specialization in the diversified branches of geologic research and the voluminous publications in many of these branches is unfortunately responsible for inability even among professional geologists to keep closely in touch with work outside of a particular field. Mineralogists, crystallographers, petrographers, vertebrate paleontologists, palcobotanists, micropaleontologists, seismologists, oceanographers, geomorphologists, and economic geologists of many special sorts — to mention only part of the list — devote most of their time to one division of geologic science, and divergence rather than convergence is the inevitable present trend. It follows that in the limits of a short article, such as this summary of geology in 1938, notice of only a small number of representative subjects can be given, but it is necessary to avoid condensation to a point of rather meaningless enumeration.

Oceanography.

Greater attention than ever before is being given by geologists to problems of the floor of oceanic areas, especially the more easily reached areas of shallower depths adjacent to continental borders. Important aids in this study come from development of new instruments and techniques, as well as from interest of organizations like the Geological Society of America, oceanographic institutions, and governments which are allocating considerable sums for such research.

Beginning three or four years ago, when announcement was made of findings in rather detailed hydrographic surveys on parts of the Atlantic coastal shelf, and also off the California coast and opposite the mouth of the Congo, efforts have been multiplied to secure closely spaced soundings in many marine areas. Steep-sided canyons with the dendritic distribution pattern that is characteristic of valleys on land are found in numerous places to descend below sea level as much as 9,000 feet, and submerged deltas representing at least two cycles of building are identified in connection with some of these thousands of feet below sea level. Some of the submerged valleys are rock-walled. Some are continuations of stream valleys on land, as for example, the Hudson, but others are not. The existence of some of the submerged valleys has long been known but little attention has been paid to them. Because evidences are increasingly numerous that these deeply submerged valleys were carved by running water above sea level, and because the valleys on the east and west coasts of North America and on the cast side of the Atlantic all appear to be contemporaneous, geologically rather recent results of erosion, it seems necessary to conclude that mean ocean level has fluctuated several thousands of feet with respect to the lands during or since the time of the last great Ice Age. Removal of water to make ice sheets and return of part of this water to ocean basins by melting of the ice however, are quantitatively very inadequate as explanation.

Methods of taking core samples, 12 feet or more in depth, of ocean bottom deposits have recently supplied materials from the Atlantic floor that by alternating succession of warm water and cold water foraminiferal assemblages in the sediments are thought to show the changing conditions due to glaciation and deglaciation in Pleistocene and Recent time. On the other hand, uniformity of sediments in cores from deep areas in the Pacific Ocean, some 300 miles from shore, indicate little fluctuation in conditions of sedimentation. These cores also give a measure of the rate of sedimentation in the places sampled.

A current subject of study and discussion among geomorphologists who are interested in oceanography is a reclassification of all known types of shorelines on a genetic basis.

Historical Geology.

An important set of volumes, now in process of writing and publication, representing the summary conclusions of one of the world's leading stratigraphers, A. W. Grabau, of Peking, China, is more than half completed. This work ('Palaeozoic Formations in the Light of the Pulsation Theory') reviews features of the geologic record in all parts of the world, and, with voluminous reference to paleontologic data, undertakes to trace the chief changes in relative emergence of the continents above periodically wide-spreading seas. Proposal is made to revise the names and limits of the major divisions of the geologic column and the corresponding divisions of geologic time to accord with evidences of great marine and continental 'pulsations.' Each pulsation period witnessed more or less widespread submergence of continents, followed by withdrawal of seas with accompanying erosion of lands. In spite of the soundness of most of Grabau's interpretation, the inertia of long usage of familiar old terms will not allow general adoption of this new classification and nomenclature, especially since some of the innovations among terms are not too well chosen.

The necessity for very careful segregation of paleontologic evidences according to the exact geologic horizons from which fossils may be collected, and the similar care that must be exercised in correlating rock strata on the basis of the order of succession, lithologic characters, and fossil contents, are well shown by a review of the famed and highly controversial 'Laramide problem,' reported in 1938 by E. Dorf. This problem, which is mentioned in almost all American textbooks of historical geology, has to do with the boundary between Mesozoic and Cenozoic deposits in the western interior of North America and bears on the geologic dating of the Laramide (or Rocky Mountain) mountain-building. Dinosaurs, the characteristic great reptiles of Mesozoic time, have been thought to be represented by skeletal remains in rocks that also yield typical floras of early Cenozoic time; this association could only mean contemporaneous existence of surviving dinosaurs and newly appeared, modern types of trees and shrubs. The 'transition beds' were considered by some geologists as Mesozoic and by others as Cenozoic. Sifting out by means of new field studies the actual occurrences of the fossil reptile bones and plant remains shows that the flora of the dinosaur-bearing deposits is actually quite distinct from that of other plant-bearing beds with which these had been confused, and it becomes possible to settle the position of the geologic boundary between these two eras, as well as to resolve certain questions about the age of crustal deformations in the Rocky Mountain region.

Studies of the age of rocks by means of measurement of accumulated lead produced by disintegration of radioactive minerals have been supplemented in late years by effort to define also the helium that is similarly produced by the disintegration. This latter method offers difficulties because of the mobility of the gas, but it is applicable to many rock samples where determination of radium-produced lead is not practicable. Recent independent remeasurements by a number of analysts have shown that previously published age determinations, secured from use of the helium method, are slightly too great. The revised helium scale shows ages of different rock samples ranging from 3 to 1,500 million years, and this accords well with results on other samples by the radium-lead method.

Paleontology.

Studies of fossils are of fundamental importance in the advance of geologic knowledge, and publications of 1938 giving results of paleontologic research are numerous. Mostly, however, these are highly technical reports that are without interest for the layman. This does not mean that the subject matter is devoid of interest, generally speaking, but rather that treatment is much too detailed, too greatly bound by requirements of scientific precision, and too universally given in specialized terminology to be understood or widely appreciated. It is unfortunate that this storehouse of information concerning the varied forms of past animal and plant life on the earth is so largely locked in the vault of forbidding, though often beautifully illustrated, publications.

Work on fossil plants that is specially worthy of notice includes a monograph on one of the oldest known types of conifers, named Lebachia (former Walchia), by the Swedish paleobotanist, R. Florin; these plants were widespread in cool, relatively dry lands of Upper Carboniferous and Permian time. One of the largest known floras of Jurassic age from eastern Greenland has recently been described by T.M. Harris. The most ancient of all known plants, possibly excepting bacteria, are varied sorts of algae from Proterozoic rocks. Those found in northwestern Montana, in the Glacier Park area, have recently been described by C. L. and M. L. Fenton.

Publications.

A few outstanding contributions to invertebrate paleontology recently published, are: monographs on certain families of fossil Foraminifera by J. A. Cushman; the remarkable succession of 'wheat grain' foraminifers called Fusulinids which are important zone fossils in Permian rocks of Texas, by C. O. Dunbar and J. W. Skinner; Cambrian and early Ordovician brachiopods, by E. O. Ulrich and G. A. Cooper; late Paleozoic Sectionid Clams (scallops), by N. D. Newell; and the complexly-organized chambered cephalopods called Ammonoids — Devonian by A. K. Miller, and Carboniferous-Permian by F. B. Plummer and G. Scott. Increasing attention to use of fragmentary fossil remains, representing various sorts of invertebrates, is proving valuable in many cases where other material is inadequate for correlation of beds. In 1938 there appeared the first two sections (Wenz: Gastropods; Bulman: Graptolites) of a projected 20-volume work on Invertebrate Paleontology, with authorship distributed among leading specialists of the world; published in Germany under guidance of O. H. Schindewolf, one of the issued sections is in English, another in German, and other divisions will use these languages or French, according to choice of authors. Of outstanding importance as a reference and advanced text, this series is intended to contain diagnoses and classification of practically all known genera of fossil invertebrates.

Among contributions to vertebrate paleontology, special notice is due several studies of fossil fishes, because greater relative advance in knowledge appears lately to have been made here than in other branches. One of these works (D. M. S. Watson: 'The Acanthodian Fishes') especially, fills a gap in furnishing information on the oldest and most primitive known gnathostomes, Silurian to Permian in age; these are treated as a group that is equal in rank to Pisces, the fishes proper. An enlarged and rewritten edition of W. B. Scott's 'History of Land Mammals in the Western Hemisphere,' which has been, since 1913, one of the most widely read books on Tertiary vertebrates, brings this important, well-illustrated treatise abreast of recent studies of fossil mammals.

Fossil Remains.

The Great Plains region of the central western United States, especially in parts of Nebraska and South Dakota, has furnished numerous skeletons and fragmentary remains of three-toed horses, camels, and other mammals of many kinds, now extinct, that roamed this country during the past 20 to 30 million years. Search for these fossils and studies of them by American paleontologists have made the evolutionary history of mammals much better known than would have been possible by work in other continents where remains of these animals are less abundant and not so well preserved. Recent researches in this field are resulting in a more exact determination of the geologic sequence of the mammalian faunas, which is important in studies of the evolution of individual stocks, in defining geographic or environmental modifications, and in reaching conclusions as to certain intercontinental migrations that are otherwise indicated by occurrence of closely-related animals in distant parts of the earth.

A discovery that is of intrinsic interest, and one that aids greatly in precise correlation of local deposits of fossil bones in the plains country, as well as in work to determine geologic structure that affects water-supply and that may indicate oil or gas occurrences in deeper rocks, is identification (M. K. Elias) of several zones of fossil grass seeds in the Tertiary deposits of Kansas and neighboring states. These are silicified minute fossils that are very widespread and in places very abundant. The fact that different kinds of these seeds mark various levels in the strata serves to define distinct ages of accumulation of the sediments and to furnish evidence of relative age of vertebrate bones found with them locally.

Further investigations of geologic evidence as to age of the 'Minnesota girl,' discovered by workmen on highway grading in 1931, indicates general agreement that this skeleton is about 20,000 years old and belongs near the beginning of man's advent in North America; this view is contested, however, by at least one glacialogist (Antevs). Human artifacts, estimated to be about 10,000 years old, were recently found in western Kansas, and evidences of early man as represented by the so-called Folsom culture, of about this age or older, are increasing by finds in several localities.

Petrology.

Very noteworthy in this branch of geologic science is the completion during 1938 of a monumental work by Albert Johannsen, emeritus professor of petrography at the University of Chicago, on the description and classification of the igneous rocks of the world. This is a treatise in four large volumes, 'A Descriptive Petrography of the Igneous Rocks,' that brings together practically all analyses in world literature giving chemical and mineralogical composition of igneous-rock specimens. Not least among difficulties confronting petrographers are the problems in making a truly satisfactory classification of the multitudinous types of rocks now known and the myriad names that are applied, mostly without system; these features are clearly shown in Johannsen's extremely valuable compilation and original contributions.

Another noteworthy publication in this field is a revision by A. K. Wells of the well-known textbook of the late F. H. Hatch, eminent British petrologist; this work, 'Petrology of the Igneous Rocks' presents a rational classification and simplified nomenclature that are to be commended, and in the latter part gives a clear account of igneous activity in the British Isles during geologic time. The first comprehensive treatment in English of the so-called petrofabric technique in study of rocks, developed in Germany by Sanger, has just been written by E. B. Knopf and E. Ingerson ('Structural Petrology'), and issued as a monograph of the Geological Society of America. Study of the orientation of mineral constituents in rocks permits determination of their structural history and has many important applications in theoretic and economic investigations.

For several years an increased attention has been given to the study of the sedimentary rocks, both from the standpoint of sedimentation and from petrographic research. This work is important in several lines of economic application and in stratigraphic interpretation, as well as in achieving better balance within the field of petrology as regards knowledge of the three main classes of rocks, igneous, sedimentary, and metamorphic. A well-written book by W. C. Krumbein and F. J. Pettijohn ('Sedimentary Petrology') that has just appeared fills a widely expressed want.

Geophysics.

A variety of instruments and methods are now successfully being applied to the determination of geologic features that are only partially known or undeterminable from surface work. Chief among geophysical tools are the seismograph, torsion balance, gravimeter (for direct measurement of gravity), magnetometer, and various sorts of electrical resistance or conductivity instruments. Subsurface delineation of such geologic features as contacts between rock formations, sheared zones, faults, occurrence and position of quartz veins, silicified zones, ore bodies, water-bearing sand, gravel or rock, and thickness of overburden above bed rock, is possible with varying degrees of precision. Work of this sort is being done mainly by private concerns but is also conducted on an increasing scale by Government agencies. Millions of dollars invested in geophysical work in American oil fields, combined with geologic surface and subsurface work, is responsible for continued discoveries of needed petroleum reserves. In South Africa, geophysical studies have revealed an 18-mile extension of the Rand gold-bearing 'reefs' and it is certain that if the gold content in this yet unworked area is approximately as rich as in the mined district the world's annual production of gold will be greatly increased. Magnetic methods, in exploration for iron ore have long been applied successfully in North America, South America, and Europe. Copper, nickel, lead, zinc, and gold are being found by use of electrical methods, and similar technique is showing the location of potable water supplies in arid regions of the United States, Spain, Africa, and Palestine.

A new and promising type of investigation in the search for old fields is soil analysis to determine presence of ethane or certain other hydrocarbons, with measurement of their very minute quantities. Locally concentrated occurrence of the hydrocarbons signifies slow seepage from underground reservoirs, which, in light of data as to distribution of hydrocarbon-rich samples and in some cases with consideration of electrical resistance anomalies, may be used to guide drilling.

Seismology.

The chief recent advances in seismology include: installation of several new stations and the modernization of old ones, development of earthquake information services, inauguration of a strong motion program providing records for studies of earth structure, work on ground vibration, study of the effect of regional anomalies in gravity on transmission time of earthquake waves, and special triangulation and leveling work in order to furnish observational-control data in regions subject to earthquakes (N. H. Heck). Several seismic stations equipped with identical instruments of high magnification that lately have been established in New England show a considerable number of local quakes for which the epicenters have been determined; the new data, supplemented by future records, are expected to throw light on problems of seismicity of the region. Data on some 300 reliably recorded 'deep focus' earthquakes, emanating from depths of 100 kilometers (about 61 miles) or more within the earth, indicate a certain periodicity of occurrence that is correlated with tidal stresses.

Structural Geology.

One of the most important recent contributions to knowledge of the nature of mountain building appears to be the discovery by V. Meinesz of extraordinary negative anomalies (gravity below normal, indicating less than average mass in the underlying earth crust) in the vicinity of island arcs, like that of the Lesser Antilles. A belt of strong negative anomalies is now known to extend eastward from Cuba, north of Haiti and Puerto Rico, around the outside of the Lesser Antillean arc, crossing Barbados and Trinidad, and continuing westward north of the South American coast to Colombia. This belt is interpreted as caused by the downbuckling of the upper crust, some 15 miles in thickness, which is reflected partly in a deep trough that is the topographic expression of the buckle and partly by a ridge (produced by upward pushing of weak materials) flanked by deep troughs. There is evidence of thrusting and overturning of rocks in an outward direction on both sides of the axis of the belt of negative anomalies, and volcanic activity, numerous earthquakes, and faulting especially characterize this belt. The observations indicate a mountain chain in process of development.