Part 12

The geological record for Pleistocene time is not as complete as one might imagine. Numerous localities have produced representative fossils but the yield is rarely large enough to solve many of the riddles which are constantly arising as investigation proceeds. Aside from those areas which bordered the retreating ice cap and where living conditions were far from favorable, the sedimentary deposits of this period are not continuous over large areas. Many Pleistocene fossils are found in stream channel beds which are always subject to removal by subsequent floods.

There is abundant evidence to indicate that the great elephants of Pleistocene time were hunted by primitive Americans whose only weapons were darts or spears tipped with points of stone. A skull and the lower jaws of several mammoths are shown here.]

Isolated patches of fossil-bearing sediments frequently record the migration of animals in unmistakable terms, but the details of the wanderings and the conditions encountered in the newly established habitats are often left in doubt. To correlate the facts revealed at one locality with findings at other places and, if possible, to date all prehistoric events with a greater degree of accuracy are among the major tasks of current investigations.

THE AGE OF MAN

The Pleistocene or “Ice Age,” and the Recent period in which we are living at the present moment are not sharply separated by any event readily recognized or dated, and the two combined are of very short duration as compared with other periods more clearly established by the passing of centuries. Together they comprise the Age of Man as commonly recognized, with about a million years representing the Pleistocene period, some ten to twenty thousand years the Recent. When geologists of the nineteenth century suggested that the coming of man should be regarded as the beginning of a new era, the name Psychozoic was proposed, and to some extent this term has been applied to the present period. More in keeping with other period names is Holocene, meaning entirely recent. Common usage, however, applies the simple term Recent to this unfinished chapter which is also without a clear-cut beginning.

Zoologically, man is merely one of the creatures that arrived in the course of time, along with other mammals. Just when he arrived and how he looked at the time of his coming cannot be determined from a study of fossils. Perhaps it is of no importance. There is nothing to indicate his existence before the Cenozoic, no completely satisfactory proof of existence before the Pleistocene period. As with other inhabitants of the earth, it is probable that he became prominent only after a great deal of competition with other creatures which kept his ancestors submerged for thousands of years. The Ice Age, with its check upon the progress of competing animals, undoubtedly gave him an advantage. His superior mentality enabled him to overcome adversity by methods not available to other mammals; his inventive and mechanical genius must have been greatly strengthened by his experience during this interval.

At about this point, where prehistory begins to merge into history, the geologist and paleontologist must let other interpreters carry on. Archeologists and anthropologists take up the work, and through their efforts many details have been added to our knowledge of the human race. The study of biology, which is the science of life, has provided an instructive viewpoint that enables us to see ourselves against the vast background built up by investigations into the nature of the earth and its ancient inhabitants. This science deals with living creatures as organisms—plants and animals so organized as to be capable of existence only in an environment which provides exact life requirements.

The Age of Man has been variously characterized as an age of soul, of higher intelligence, of culture, and finally, of civilization, freedom and democracy. The “crowning glory” of the organic world is pictured in history as a creature who has busied himself for thousands of years with the building up and tearing down of civilizations. Prehistory reveals this habit as something unique in the human character, for there is no other organism that has specialized so persistently in the creation of its own environment, no other that has had the combined power and talent to produce so much change.

More than anything else, the prehistoric record is a lesson in adaptation, which in its broadest sense means fitness for life under particular conditions, and always subject to organic law. Man’s efforts to bring about an adjustment between himself and his civilization have centered largely on the method of forcing himself into the mold that happens to be present, one pattern today, another tomorrow. No creature of the past has had to adapt itself to anything so radically new or so thoroughly revolutionary. The vital problem now is whether this man-made environment will prove helpful or disastrous.

Though one of its names is “culture,” it has grown sporadically and unevenly, with little evidence of the cultivation that is implied and required. Parts have been expanded to extraordinary proportions while others equally essential have been retarded in their growth. A more intelligent handling of this environment factor seems to be possible, and the present mania for “organization” may become tempered with an awakening consciousness of organic requirements where organism and environment are involved. Once we grasp the idea that “culture” results from man’s effort to improve his living, by putting into his environment something that was not there before—then, surely, this history of a billion years of living, and as many “ways of life,” should teach us something we ought to know as we go into an all-out endeavor to teach a whole world how to obtain a one-and-only way.

We may stand at the beginning of an era for which an appropriate name has not yet been suggested. Civilization, on the other hand, may provide only a minor epoch to be added in some remote time to the story of fossils.

SUPPLEMENTARY READING

The literature pertaining to fossils is widely scattered and usually too technical for the layman. It is better to use the resources of the nearest library than to feel that a specified list of books is necessary.

Any textbook on geology, zoology, or botany will provide helpful information. Most books of this type will be found interesting and readable if used to solve definite problems suggested by the student’s immediate curiosity. Very few can be read from beginning to end without a great deal of effort and discouragement.

The following have been prominent among the books consulted by the author:

Textbook of Geology; by Pirsson and Schuchert. This work has undergone several revisions and currently appears in two volumes: Physical Geology by Longwell, Knopf, and Flint; Historical Geology by C. O. Dunbar. Published by John Wiley & Sons. (Historical geology covers the entire range of prehistoric life—plant, invertebrate, and vertebrate.)

Historical Geology (The Geologic History of North America); by Russell C. Hussey. Published by McGraw-Hill. Concise, interesting, and informative.

Geology and Natural Resources of Colorado; by R. D. George. Published by the University of Colorado. Contains an excellent summary of the historical geology and sedimentary formations of Colorado.

Vertebrate Paleontology; by Alfred Sherwood Romer. Published by the University of Chicago Press. This is one of the most comprehensive and up-to-date treatments of the subject for students desiring to go beyond the elementary stage.

A History of Land Mammals in the Western Hemisphere; by William Berryman Scott. Published by The Macmillan Company. This well-known account of living and extinct mammals is one of the favorites among students.

The Age of Mammals; by Henry Fairfield Osborn. A classic in this field of literature, but for advanced reading. The book is now out of print.

The Dinosaur Book; by Edwin H. Colbert. Published by the American Museum of Natural History, New York. An illustrated story of amphibian and reptilian evolution.

Down to Earth; by Carey Croneis and William C. Krumbein. Published by the University of Chicago Press. An excellent popularization of the earth sciences—geology and paleontology.

Lexicon of Geologic Names of the United States; compiled by M. Grace Wilmarth. Bulletin 896 (in two parts) of the United States Geological Survey. A rich source of information concerning the age, character, and distribution of geologic formations, with numerous references to fossil-bearing beds.

Bibliography of North American Geology (including paleontology); various bulletins of the United States Geological Survey. Where library facilities provide access to the technical literature of museums, universities, and scientific societies, this is a valuable aid in locating publications dealing with original work in paleontology. Bulletins 746 and 747 cover the years between 1785 and 1918; Bul. 823 (1918-1928); Bul. 937 (1929-1939); Bul. 938 (1940-1941); Bul. 949 (1942-1943); Bul. 952 (1944-1945); Bul. 958 (1940-1947); Bul. 968 (1948); Bul 977 (1949). Preparation is a continuous process with recent bulletins appearing at one or two year intervals.

Ancient Man in North America and Prehistoric Indians of the Southwest; by H. M. Wormington. Published by Denver Museum of Natural History, City Park, Denver 6, Colorado. Both volumes contain authentic and up-to-date accounts of early American cultures.

MAPS

Geologic Maps. United States Geological Survey: map of the United States (1932); map of Colorado (1935). Geologic maps of a few other states are available; information regarding these may be obtained from state universities or state geological surveys.