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.