Geology, Vol. 1 [of 3]

by Thomas C. Chamberlin; Rollin D. Salisbury

Current opinion does not recognize a mental element as residing in the plant world, and it is divided as to the degree of its development in the lower animal kingdom, but its influential presence in the higher animal orders and in man is beyond legitimate question. Two phases are to be recognized: (1) the material work done under the stimulus and direction of mental impulses, as, for example, excavations, transportations, changes of drainage, removal of forests, cultivation of soil, etc., and (2) the intellectual work of the faculties themselves irrespective of material changes. In one view, geology is a purely material science concerned solely with the formation of the earth and with the physical development and relations of its inhabitants. In another, geology is a comprehensive historical science concerned with every phase of the world’s history, and certainly not least with the higher forms of life development, with their psychological, sociological, and other phases of mental attainments, since these are the highest output of the earth’s evolution. The latter seems to us the more comprehensive view.

(1) The material effects of the mental element.—Lyell long since urged that the direct work of man in changing the face of the earth was slight compared with that of the contemporaneous inorganic agencies. He called attention to the relative insignificance of the quarries, pits, cellars, and other excavations of man, compared with the work of streams, waves, and other inorganic agencies. There is justness in this view, but it needs qualification. It is to be observed that the mental era has but just begun, and that its effects are increasing with a rapidity quite phenomenal when measured by the slow pace of most geologic events. The excavations and transportations of material to-day show an enormous advance on those of Lyell’s day, which was, geologically speaking, but a moment ago. The mile-tons of industrial freightage in the Mississippi basin are to-day not wholly incomparable with the drainage transportation of the same area a century ago. A century ago is named, because the surface was then covered with natural vegetation, and the normal effect of surface erosion, independent of man, was then experienced. At present the indirect effects of man’s action are mingled with those of natural processes, and these indirect effects are probably much more important than the direct ones. The removal of the native vegetation and the cultivation of the soil expose the surface to wash to a degree far beyond that prevalent when the surface was prairie sod, or leaf-carpeted forest, and denudation and transportation have been greatly multiplied in consequence. Not only has this cultivation increased the exposure to erosion, but, by increasing the rate of run-off, it has added to the erosive power of the streams. The ditching of swamps and other tracts of retarded drainage has contributed to this acceleration. The naked, soil-less uplands of some of the once populous kingdoms of the Orient, notably portions of Syria and Greece, are sad witnesses of the accelerated erosion that attends cultivation. The erosion of certain southern fields of the United States in the last forty years is another striking illustration. It is doubtful whether some parts of this region suffered as much erosion in the preceding five centuries as they have during the last one. On the other hand, some compensation is found in the reservoirs established for water-power, and in artificial devices for retarding and steadying stream flow.

In the light of considerations such as these, man may well be regarded not only as a potent geological agent, but as dangerously so to himself. The hope is that the intelligence that has wrought a change of surface conditions serviceable for the present, but dangerous to the future, will be so enlarged as to inspire a still more intelligent control of surface conditions which shall compass the future welfare as well as transient benefit.

Human modification of the animal and vegetal kingdoms.—Man’s agency is also coming to be felt powerfully in the modification of the plant and animal life of the land and even to some extent of the sea. The larger animals that are not propagated by man are fast approaching extinction. At the present rate of extension of man’s dominion, a century or so will see the disappearance of nearly every large mammal and reptile that he does not choose to protect or propagate. By way of compensation, certain selected animals are increasing and will doubtless continue to increase. The result is, therefore, likely to be a peculiar assemblage of animal life dependent strictly on the choice of a dominant type, a state of things that has apparently never occurred in an equal degree in the past history of the earth. How far the minor forms of life, especially the insect life, and the denizens of the sea, may be brought under this monopolistic control may not be predicted so easily.

A similar profound transition in vegetation is being forced by man. The native vegetation is rapidly being replaced by selected varieties, and by varieties that take advantage of conditions furnished by man. As the agricultural control of the earth becomes more complete and effective, a result toward which very rapid progress is being made, a new flora of man’s selection will very generally prevail over the whole land surface of the globe. It is doubtful whether at any time in the history of the earth changes of flora and of fauna, and of surface, have been more rapid than those that are now taking place under the accelerating influence of man’s action, and this accelerating influence springs not mainly from automatic or instinctive reaction, but from conscious impulse and intelligent direction.

(2) The psychological factors as such.—Are the introduction and the evolution of the psychological factors themselves to be regarded as subjects of geological study? We shall find that, at the outset, the geologic record is a complete blank so far as clear evidence of terrestrial organisms actuated by their own intelligence is concerned; that later, organisms with some apparent consciousness and intelligence appeared, and that the mental element increased apace unto its present attainment. We know that relationships of a sociological nature arose in apparent feebleness, and gradually evolved into more definite, higher, and more complex forms. By sociological factors we mean merely those conscious relations which one organism bears to another, of which the parental and the gregarious impulses are two fundamental expressions. For manifest reasons, the introduction and evolution of the psychological and sociological factors themselves have received little direct recognition as a portion of geological studies. The record of such factors in the fossils of past ages is necessarily obscure and imperfect, and the interpretation of what there is lacks certainty and precision. None the less, this psychological record, with all its imperfections, is beyond valuation, and must, we think, come to be an indispensable factor in the study of psychological and sociological evolution, for it shows, what nothing else can show equally well, the extremely prolonged history of that evolution, and it gives hints of modes and means which no study of existing stages can equally reveal. The organization of the Cambrian trilobites, for example, implies no small development of the senses and of the coordinating faculties even at that early stage, and a study of the relations of these to their fellow creatures opens up the first known chapter in the sociological record of the earth’s inhabitants. From this stage onward the progress in the development of the higher faculties, and of the sociological relations of the leading forms, is one of the most instructive phases of the great history. Such a study reveals the fact that many questions, narrowly supposed to be purely human, have had their prototypes in the earlier experiences of the animal kingdom. Some of these questions have found solutions, temporary or permanent, which passed under the test of ages to whose length human experience affords no parallel, and have received the sanction or disapproval of such tests according as they were well or ill adapted to the actual conditions involved. If one seeks the lessons of history in the largest sense, he cannot wisely neglect the prolonged record of the great biological family.

II. SPECIAL CONTRIBUTIONS OF THE ORGANIC KINGDOMS.

An essential part of the historical chapters of the second volume will consist of the description and illustration of the life progress of the successive periods. It will suffice here to give a preliminary synopsis of the kinds of record made by the several groups of plants and animals.

A. Contributions of the Plant Kingdom.[290]

The record of plants in the early geological ages is extremely imperfect. In the very earliest times the conditions seem to have been wholly unsuited to the preservation of any relics of life; but even after animal remains were abundantly preserved in the sea sediments, the plant record was still very meager for a long period. This was probably due in the main to two chief causes: (1) the probable softness and perishability of the early types of vegetation, and (2) the fact that vegetation is preponderantly terrestrial. At no time has marine vegetation reached a high development. Land conditions favor decomposition, transportation, and erosion, and through these, destruction; and only under rather occasional and exceptional conditions did the old lands leave a good record of their life. Nevertheless all the great groups of plants, viz. the Thallophytes (algæ, fungi), the Bryophytes (mosses, liverworts), the Pteridophytes (ferns, horsetails, lycopods), and the Spermatophytes (gymnosperms, angiosperms) have left some record.