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.