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.