EX LIBRIS William Healey Dall Division of Mollusks Sectional Library ee cal = Ps 1 OUTLINES OF GEOLOGIC HISTORY THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS Agencies CAMBRIDGE UNIVERSITY PRESS LONDON AND EDINBURGH F, A. BROCKHAUS LEIPZIG AND PARIS QE GS/ ae OUTLINES OF GEOLOGIC HISTORY Moll. WITH ESPECIAL REFERENCE TO NORTH AMERICA A SERIES OF ESSAYS INVOLVING A DISCUSSION OF GEOLOGIC CORRELATION PRESENTED BEFORE SECTION E OF THE AMERICAN ASSOCIATION FOR THE ADVANCE. MENT OF SCIENCE IN BALTIMORE, DECEMBER, 1908 SYMPOSIUM ORGANIZED = Ohetistion, of Mollusks BAILEY WILLIS Sectional Library COMPILATION EDITED BY ROLLIN D. SALISBURY THE UNIVERSITY OF CHICAGO PRESS CHICAGO, ILLINOIS a — MAY 27 1988 LIBRARIES CopyrRiGHT 1910 By THE UNIVERSITY OF CHICAGO All Rights Reserved Published July 1910 Composed and Printed By The University of Chicago Press Chicago, Illinois, U.S.A. PREFATORY NOTE The essays in this volume were presented before Section E, of the American Association for the Advancement of Science, at the meeting in Baltimore in December, 1908. ‘The original plan of the papers involved the formulation of the principles of correlation, as applied to the formations of different periods. This plan was conceived by Bailey Willis, then vice-president of Section E, and was carried out with much success. The several chapters have appeared in the Journal of Geology, since their presentation at Baltimore. They present in broad outlines a summary of certain phases of existing knowledge of North American geology, and are now bound together in the belief that students of geology in this country and abroad will welcome them in this more convenient form. ‘The paleogeo- graphic maps by Mr. Willis form a valuable part of the volume. JUNE, I9I0 , « 2 ° . - \ . fi i ‘ i > : Bs ; » 7 PLE IV. VI. Vibe VIII. ADEE eOr CONTENTS PRINCIPLES OF CLASSIFICATION AND CORRELATION OF THE PRE-CAMBRIAN ROCKS By CHARLES RICHARD VAN HISE THE BASIS OF PRE-CAMBRIAN CORRELATION By FRANK D. ADAMS EVOLUTION OF EARLY PALEOzOIC FAUNAS IN RELATION TO THEIR ENVIRONMENT By CHarLEsS D. WaALcottT EARLY CAM- PALEOGEOGRAPHIC Maps OF NORTH AMERICA BRIAN AND LATE CAMBRIAN By BatLEy WILLIS PHYSICAL AND FAUNAL EVOLUTION oF NortTH AMERICA DuRING ORDOVICIC, SILURIC, AND EARLY DEVONIC TIME By AMADEUS W. GRABAU PALEOGEOGRAPHIC MApS—ORDOVICIAN AND SILURIAN. By BatLey WILLIS CORRELATION OF THE MIDDLE AND UPPER DEVONIAN AND THE MISSISSIPPIAN FAUNAS OF NORTH AMERICA By STUART WELLER PALEOGEOGRAPHIC MApS—DEVONIAN AND MISSISSIPPIAN By BaILEy WILLIS UppER CARBONIFEROUS By GEoRGE H. Grirty THE Upper PALEOzOIC FLORAS, THEIR SUCCESSION AND RANGE : By Davip WHITE PALEOGEOGRAPHIC MApS—PENNSYLVANIAN By BatLEy WILLIS THE FAUNAL RELATIONS OF THE EARLY VERTEBRATES By S. W. WILLISTON PALEOGEOGRAPHIC Maps—LATEST PALEOZOIC, TRIASSIC >] >) AND LATE JURASSIC By BatLrey WILLIS PAGE 28 g2 I21 124 She) 161 163 176 Vill Xe xae XII. XIII. XIV. XV. XVI. TABLE OF CONTENTS SUCCESSION AND DISTRIBUTION OF LATER Mesozoic INVER- TEBRATE FAUNAS IN NorRTH AMERICA By T. W. STANTON PALEOGEOGRAPHIC MAps—LOWER CRETACEOUS AND UPPER CRETACEOUS By BatLtrey WILLIS SUCCESSION AND RANGE OF MESOzOIC AND TERTIARY FLORAS ! 2 By F. H. KNOWLTON CONDITIONS GOVERNING THE EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS . By W. H. DAL PALEOGEOGRAPHIC MApsS—EOCENE-OLIGOCENE AND MIOo- CENE A By BatLEy WILLIS ENVIRONMENT OF THE TERTIARY FAUNAS OF THE PACIFIC COAST OF THE UNITED STATES By RaLtpH ARNOLD CORRELATION OF THE CENOzoIcC THROUGH ITs MAMMALIAN LIFE , E ; : By Henry F. OSBORN PHYSICAL GEOGRAPHY OF THE PLEISTOCENE WITH REFER- ENCE TO THE CORRELATION OF PLEISTOCENE FORMATIONS By Rotitn D. SALISBURY PALEOGEOGRAPHIC MAps—QUATERNARY By BaAtLEy WILLIS ORIGINATION OF SELF-GENERATING MATTER AND THE INFLUENCE OF ARIDITY UPON ITs EVOLUTIONARY DEVELOP- MENT : 5 By D. T, MaAcbouGaL DIASTROPHISM AS THE ULTIMATE BAsIS OF CORRELATION By THOMAS CHROWDER CHAMBERLIN PAGE 182 196 200 222 220 251 265 276 278 298 CHAPP ER: I PRINCIPLES OF CLASSIFICATION AND CORRELATION OF THE PRE-CAMBRIAN ROCKS CHARLES RICHARD VAN HISE A half-hour summary of the principles of classification and correla- tion of the pre-Cambrian rocks can give no more than the barest outline of the subject. In the classification and correlation of the pre-Cambrian forma- tions we lack the guide of fossils. While life existed in pre-Cambrian times, and a few fossils are found in several areas, they are not suffi- ciently abundant to serve either for the purposes of classification or correlation. How far-reaching this handicap is will be realized when this paper is contrasted with those that follow. In considering the questions of classification and correlation of the later formations, fossils occupy a paramount position. It is true that the faunal breaks are often and probably are generally dependent upon physical causes, and the latter are frequently considered; but when the determinations are made, the fauna rather than the physical factors are given first place. In the classification and correlation of the pre-Cambrian our sole criteria are physical. Therefore we have for the discriminations only those guides which for the fossiliferous rocks are commonly regarded as subordinate. It follows that with the pre-Cambrian rocks we are on less certain ground than with the later formations. However, the very fact that fossils are not available in studying the pre-Cambrian has led the workers in this field to a careful consideration of the physical criteria and their relative value. Among the physical factors which have been used in the classi- fication and correlation of the pre-Cambrian, the following are the more important: (1) Lithological character; (2) Continuity of formations; (3) Likeness of formations; (4) Like sequence of formations; (5) Subaerial or subaqueous deposits; (6) Unconformities; (7) Relations I 2 CHARLES RICHARD VAN HISE to series of known age; (8) Relations with intrusive rocks; (9) Amount of deformation; (10) Degree of metamorphism. 1. Lithological character.—The first step in the study of rocks from a physical point of view is to determine the character of the formations, series, and groups—whether igneous or sedimentary; if igneous, whether plutonic or volcanic, acid or basic; if sedimentary, whether psephite, psammite, pelite, limestone. While according to definition a formation is essentially a lithological unit, usually this unit is more or less composite, consisting of many somewhat variable beds and often of several members of different character. Because of the variability of the elements constituting a formation, there are an indefinite number of permutations and combinations of these factors. This results in giving a given formation, series, or group special peculiarities which often enable one to recognize it even when actual connections of the various outcrops have not been observed. Accepting any of the current theories as to the history of the earth, the rocks of the earliest time are dominantly of igneous origin, and those of later time dominantly sedimentary. Since the earliest Cambrian rocks contain remains of all the great types of life, it is certain that antecedent to this time the more fundamental and the greater part of organic evolution took place. Hence in a full pre-Cambrian succession we should expect the rocks of the early pre-Cambrian to be dominantly igneous and those of the later pre-Cambrian to be dominantly sedimentary. In accordance with the natural expectation, in practically all of the great regions of the world in which the pre-Cambrian have very extensive exposures, and in which close studies have been made, we find that the basal series of rocks is dominantly igneous, and the superior seriés dominantly sedimentary. 2. Continuity of formations—Where formations in different districts are found to be continuous, they are supposed to be of the same age. It is realized that this conclusion is not absolute, for in the case of a great slanting transgression of the sea, the basal clastic deposits of the early part of the transgression may be considerably earlier than those in the later part, although the formations may be continuous. However, as yet given pre-Cambrian formations have THE PRE-CAMBRIAN ROCKS 3 not been traced to sufficiently great distances to introduce important errors upon this account. 3. Likeness of formations.—Where in different districts there are like formations, this is of assistance in correlation. Thus, if in several districts of a geological province but a single limestone forma- tion is observed in any one, and the limestone of the different districts has the same peculiarities, there is a natural tendency to suppose all the limestone to be part of a single formation. However, the criterion of lithological likeness alone is not sufficient to establish identity. This is illustrated by the three iron-bearing formations of the Lake Superior region. Because these formations were of such an excep- tional and peculiar character, and were so remarkably alike, it was supposed for a long time that they were of the same age. For a number of years this mistaken belief was a serious hindrance to an understanding of the succession and structure in this region. The weakness of lithological likeness in correlation is due to the fact that the same set of physical conditions has frequently occurred during geological time, and thus formations practically identical even in the combinations of their variations, including color, banding, nature of beds, etc., have been produced again and again. 4. Like sequence of formations.—Similar sets of formations in the same order furnish a criterion for correlation, of much greater con- sequence than the likeness of a single formation. But even this criterion has severe limitations, for similar sets of formations in the same order may have been deposited a number of times during a geological era; for instance, when a sea transgresses over a land area there are normally formed in order a psephite, a psammite, a pelite, and a non-clastic formation, and frequently over this, another pelite. Several such similar sets of formations are known in the pre-Cambrian in a single geological province. 5. Subaerial or subaqueous deposits.—Closely connected with the third and fourth criteria is the question as to whether the deposits were laid down under air or under water. It is clear that the conditions of deposition of these two classes of rocks are so different and the nature of the formations which may be contemporaneous so variable, that there is great difficulty in correlating the two. Also it is plain that the difficulties in correlating disconnected continental deposits 4 CHARLES RICHARD VAN HISE are scarcely less great. Only recently has serious study been under- taken to discriminate subaerial and subaqueous deposits. This subject will not be gone into here, since it is one which has been recently discussed in several extended papers. I may, however, speak of one point. So far as we can yet determine the subaerial deposits are in general not so well assorted nor so likely to be sharply separated into distinct formations as the subaqueous deposits. This statement is believed to hold although it appears that under exception- ally favorable conditions the aerial deposits may be pure quartzose sands. Consequently cleanly assorted quartzose sands, pure lime- stones, and series composed of sharply contrasted formations are regarded as strongly favoring the idea of subaqueous deposition. As yet there is no evidence that air has the discriminating capacity which water has in producing cleanly assorted sands. If it is difficult to discriminate subaerial or subaqueous deposits, it is much more difficult to discriminate subaqueous deposits of the inland lakes and seas from those of the ocean. 6. Unconformities.—Unconformities are of great assistance in classification and correlation. It has been intimated that the great physical movements producing unconformities are frequently the real causes of faunal changes. Irving was the first fully to realize the importance of unconformities in correlation. ‘The criteria by which unconformities are determined and their magnitude and significance analyzed cannot be discussed in a short paper. Those interested in this aspect of the subject must be referred to the original discussions.* It should be remarked, however, that unconformities may have a very variable extent and significance. It is now realized that a sharp orogenic movement may take place resulting in uplift, erosion, subsidence, and therefore discordance of strata, which may not affect an adjacent area. Thus it should clearly be understood that it cannot be assumed that unconformities due to orogenic movements are more than of district extent. There are, however, great movements of uplift and subsidence which are continental and may be even inter- tRoland Duer Irving, ‘On the Classification of the Early Cambrian and Pre- Cambrian Formations,” Seventh Annual Report, U.S. G.S., pp. 365-454; Charles Richard Van Hise, ‘‘ Principles of North American Pre-Cambrian Geology,” Sixteenth Annual Report, U.S. G. S., pp. 724-34. THE PRE-CAMBRIAN ROCKS 5 continental. Unconformities due to movements of this kind may have a very wide extent, and may thus be used for correlation from province to province, or possibly even from continent to continent. But in order that this may be fully done, it is necessary to show that the unconformity upon which correlation is based is an extensive one. As yet insufficient careful study has been made of known uncon- formities from this point of view. Here is a great and fundamental field for investigation. If the known unconformities of the world were broadly studied, it is probable that many can be determined to be local, others to be provincial, others continental, and a few inter- continental. No more important determination than this remains to be made in geology. So far as I can see until this work is done there will be no very close correlation of pre-Cambrian formations from province to province and from continent to continent. 7. Relations to series of known age.—The relations of a formation, series, or group, to other formations, series, and groups of known age are of very great assistance in correlation. Frequently a formation, series, or group may be continuous or recognizable in the different districts of a geological province when other formations, series, or groups are not continuous. The position of the latter with relation to the former, whether above or below, and if above or below, con- formable or unconformable, are valuable helps in correlation. ‘Thus the Keweenawan is practically continuous about the entire Lake Superior basin. This is the only series of which this is true. The position of the series called Upper Huronian immediately but un- conformably below the Keweenawan in different districts in con- nection with other facts is of great significance. 8. Relations with intrusive rocks.—The older is a series the more intricately is it likely to be cut by intrusive rocks, and this relation is of assistance in correlation in connection with other criteria. Ifa series is intricately cut by igneous rocks, all of which stop at a definite horizon, this is strong evidence that the adjacent rocks free from such intrusives are later and probably belong to a different series. 9g. Amount of deformation—The amount and nature of the deformation are of assistance in correlation within limited areas. Upon the whole, the older a series the greater and more intricate the deformation. The difference in the amount of deformation in the 6 CHARLES RICHARD VAN HISE pre-Cambrian series wherever there is a somewhat full succession of formations is sufficiently great to make this an important factor in the classification and correlation of the formation. 10. Degree of metamorphism.—The amount of metamorphism is a factor in correlation. Upon the whole, the older a series the more likely it is to be metamorphosed, but this criterion has severe limitations, since within comparatively short distances the closeness of folding and the quantity of intrusives may greatly vary, and these are very important factors in metamorphism. The worker among the pre-Cambrian rocks must have a very thorough understanding of the principles of metamorphism and the nature of the transforma- tions through which rocks go. For, in working out the stratigraphy of the pre-Cambrian, if the criterion of the original character is to be used, it is necessary to know the rocks which the now greatly meta- morphosed varieties represent. GENERAL STATEMENT In actually working out the succession of formations, series, and groups in the different districts of a geological province and in corre- lating them, all of the above criteria must be used. It is in judgment in appreciating the value of each of these criteria and their combina- tions that the skill of the pre-Cambrian stratigraphical geologist appears. To this time, from my point of view, the only divisions of the pre- Cambrian which have been proved to be general, if not world-wide, are those of the Archean and the Algonkian. This subject I shall not take up in detail, since I have recently discussed it in another address.? However, it may be said in summary that the Archean is a group dominantly composed of igneous rocks largely volcanic and for extensive areas submarine. Sediments are subordinate. The Algon- kian is a series of rocks which is mainly sedimentary. Volcanic rocks are subordinate. The Algonkian sediments where not too greatly metamorphosed are similar in all essential respects to those which occur in the Paleozoic and later periods. When the Algonkian 1Charles Richard Van Hise, ‘‘The Problems of the Pre-Cambrian,” Bulletin, Geological Society of America, Vol. XLX, pp. 1-28. THE PRE-CAMBRIAN ROCKS 7 rocks were laid down essentially the present conditions prevailed on the earth. The Archean rocks on the other hand indicate that during this era the dominant agencies were igneous. The physical condi- tions had not yet become such as to lead widely to the orderly suc- cession of sedimentary rocks like those being formed today. On the whole the deformation and metamorphism of the Archean are much farther advanced than the Algonkian. The two groups are commonly separated by an unconformity which at many localities is of a kind indicating that the physical break is of the first order of importance. As evidence of this, at many places are the funda- mental difference in the character of the rocks, the greater intricacy of intrusion, greater deformation and metamorphism of the older group, and deep intervening erosion. In some localities a part of these phenomena are lacking, but the significance of an unconformity is determined by the places where evidences of its magnitude occur rather than where lacking. So profound are the contrasts between the Archean and the Algonkian in each of the great regions of the world in which the pre-Cambrian has been studied, and so similar are each of these great groups with reference to the fundamental principles discussed that it has been regarded as safe to correlate these two groups even when in distant geological provinces. In mak- ing this correlation it is not supposed that the formations of one province are of exactly the same age as those of another province, but that the formations assigned to the Archean and Algonkian respectively in any given case belong to the two great eras of the pre- Cambrian represented by the rocks of these groups. For extensive areas the Archean may be divided into Laurentian and Keewatin. These divisions are purely lithological, the former being mainly plutonic acid igneous rocks and the latter basic igneous rocks, largely volcanic. The Algonkian in many of the various geological provinces may be divided into two or more series separated by unconformities. The formations of these series are commonly sedimentary, although igneous rocks are often abundant. As a whole, to the Archean group ordinary stratigraphical methods do not apply. To the Algonkian such methods are as applicable as to the Paleozoic and later series. While the subdivisions of the Archean and of the Algonkian can 8 CHARLES RICHARD VAN HISE be frequently equated in the same geological province, as, for instance, in the case of the Upper Huronian in the different districts of the Lake Superior region, it has not been found practicable to equate them from province to province. That is to say, one cannot be certain as to the correspondence of individual Algonkian series of China, Scandinavia, and of the Cordilleran region. If, as above suggested, it becomes possible to work out the physical history of the continents so that it may be determined which of the unconformities are continental, and intercontinental, or if in the pre-Cambrian rocks distinctive faunas are found, then closer correlation of the pre-Cam- brian in different geological provinces may be possible than the Archean and Algonkian. In the meantime we must be content with the classification of the pre-Cambrian rocks in different geological provinces into Archean and Algonkian, with the understanding that the formations placed in each of these groups belong in a general way to the two early eras of the earth, during the first of which the agencies were dominantly igneous, and during the second of which the conditions had become similar to those of today. Further, within each geological province the Archean and Algonkian may be divided into series and formations which for each province are given local names. Chiara i THE BASIS OF PRE-CAMBRIAN CORRELATION FRANK D. ADAMS McGill University, Montreal That was indeed a fair and sunlit earth which our predecessors, the first geologists, had presented to them for study. The uniform strata of the newer periods of our earth’s history in their succession, well exposed, and following one another in due and regular order, everywhere contained abundant fossil remains which afforded a cer- tain clue by which correlation could be made even in widely sepa- rated areas. We, their unfortunate successors, in pursuing our studies are obliged to descend into the deeper parts of the earth where the light begins to fail and when once we pass through that last grim portal into the drear pre-Cambrian world, we enter into what these earlier geologists regarded as a hopeless chaos. Here we lose the guiding thread of life, and the darkness deepens. At first we could dimly descry but the outlines of the vast indeterminate ruins of former worlds, but as our eyes become accustomed to the darkness these become somewhat more distinct and we recognize succession even in this ruined waste. It may be that being a petrographer I overestimate the value of paleontology, but, like other things, we prize it most highly when it is lost and we are obliged to look for something to take its place. The working-out of the stratigraphical succession by detailed map; ing in special areas teaches us much, but unfortunately the areas showing such succession are usually limited and isolated and the criteria for correlating the successions in separated areas, and especially in widely separated areas, are as yet undiscovered. The vice-president of our section, Dr. Bailey Willis, in inviting me to take part in this symposium, has suggested that I should treat this subject of pre-Cambrian correlation if possible on broad lines, and I therefore venture today to follow Faust’s aspiration, “Schaw’ alle Wirkenskraft und Samen,” and present a certain aspect of the 9 10 FRANK D. ADAMS subject which I hope may at least be suggestive of a line along which some advance may be made in the correlation of these ancient rocks. In his Research in China (Vol. II, chap. viii) Dr. Bailey Willis has put forward a theory to account for the origin of continental structure. In each of our present continents there are areas which during the evolution of the continent have always tended to rise— these he calls positive elements. There are certain other areas which have always shown a iendency to sink, relatively to the adjacent masses—these he calls negative elements. The movement of these elements is due to the greater relative density of the negative elements causing them to sink, while the relatively lighter positive elements tend to rise so as to bring about an isostatic adjustment. There have been horizontal movements as well as those in a vertical direction. These are of notable magnitude and their effects areseen in the schistose structure of these once deep seated rocks and the overthrust and folded structures of the more superficial strata. The tendency toward vertical displacement has actually resulted in movement only at long intervals and during relatively short periods. Hence we may recognize cycles of diastrophism each one of which comprises (a) a comparatively brief period of orogenic and epeirogenic activity which results in elevated lands and restricted mediterranea; and (b) a comparatively long period of continental stability, which results in extensive peneplanation. ‘The critical times which bring out con- tinental structure are the epochs of diastrophic activity. During periods of inactivity the distinction between the positive and negative elements becomes less obvious and may even become obscured by extended peneplanation and marine transgression. In a subsequent paper,! the same writer outlines the positive and negative elements of the continent of North America. The Canadian Shield, which is also called Laurentia, is at once the largest and the most readily distinguished positive element of the continent. It has an area of approximately two million square miles and the true bound- ary may be traced along the St. Lawrence Valley into the deep of Baffin’s Bay and then north of the Arctic Archipelago (which is scarcely to be separated from Greenland) across the Arctic Ocean t Bailey Willis, ““A Theory of Continental Structure Applied to North America,” Bull. Geol. Soc. of America, Vol. XVIII, p. 392. a BASIS OF PRE-CAMBRIAN CORRELATION II and back to the mouth of the Mackenzie. Beneath the Cretaceous of western Canada, the margin of this element lies hidden. It ranges past Lake Winnipeg toward the state of Wisconsin, and then follows the shore of the Paleozoic mediterranean east to the Adirondacks and St. Lawrence. Now it would seem, if we select a single positive element such as Laurentia—remembering that the critical diastrophic periods will be short and the intervening periods of deposition and accumulation will be of long duration—that these epochs of diastrophism, with their development of schistose structure in the moving masses and the associated phenomena of igneous intrusion, might be employed as a basis for the subdivision of Proterozoic time, and if the element moved as a whole, might even serve as a basis of correlation over the whole vast area. Laurentia, however, has not as yet been studied geologic- ally except in a general way. Its detailed study will supply problems for generations of geologists yet unborn. Its southern margin alone, and that only in a few comparatively small areas, has been mapped in detail, but nevertheless exploratory and reconnaissance work has been carried out over almost the whole of the great expanse of this ancient continent chiefly by the officers of the Geological Survey of Canada, so that we have a good general knowledge of the main outlines, at least, of its geological history. It is proposed here to present a general statement of the results obtained, as they bear upon the history of Laurentia in pre-Cambrian times and afford a basis for pre-Cambrian correlation, making use of this principle of critical diastrophic epochs and drawing evidence from the area as a whole, rather than from a few restricted areas on its southern border. This task is rendered comparatively easy owing to the fact that a critical digest of the mass of information concerning the pre-Cambrian rocks of the great central and northern portions of Laurentia, which is found disseminated through the reports and papers by the various geologists who have worked in this great area, has recently been pre- pared by Dr. George A. Young, of the Geological Survey of Canada, who has himself traveled very extensively in this northern country. I am indebted to Dr. Young for permission to make use of this unpub- lished material, but the original papers have been consulted in the case of all the more important occurrences. 12 FRANK D, ADAMS The great expanse of Laurentia is underlain predominantly by the rocks of the Laurentian system. These consist of gneisses in infinite variety which in the majority of cases have the mineralogical composition of granite, although some present foliated varieties of rocks ranging from syenite to diorite. ‘The foliation is in some cases so faint that it can be detected only on large weathered surfaces, but generally it is quite distinct or even striking. In addition to the foliation the rock often displays a very distinct banding due to the alternation of varieties of diverse character or composition. ‘This foliation is in many, and possibly in the majority of cases, a primary structure and the darker bands very frequently represent included masses of overlying rocks, softened and in some instances partially digested. This foliation and banding was at one time regarded as a partially obliterated bedding and considered to present indisputable evidence that the rocks were of sedimentary origin. ‘These gneissic rocks are not all of the same age, for frequently one mass can be seen to cut another. In addition to these gneissic granites, syenites, and diorites, however, the Laurentian comprises other kinds of plutonic rocks of very diverse character. Thus, from Minnesota to the shores of Ungava Bay, intrusions of anorthosite are found. Several of these, for the most part distributed along the margin of the protaxis in the province of Quebec and in the Ungava peninsula, present areas of from a few miles to 10,000 square miles in extent, and represent some of the more recent pre-Cambrian plutonics, although they themselves have been cut by still later granites. In fact, it is becoming more and more evident with the progress of geological investigation that the Laurentian is a vast complex of plutonic rocks of widely varying types and differing greatly in age, although there is no evidence to show that any of them were intruded later than the close of the Pro- terozoic. Whether in this enormously extended complex, which we term the Laurentian in the northern protaxis, there still survive any primitive sediments or any portion of an original crust, through which these great bodies of intrusive rocks forced themselves, is unknown. None have as yet been distinguished with certainty, but if any do exist they are probably similar in composition to these earliest intru- sive rocks and might easily escape notice. It is certain, however, that the overlying Keewatin and Grenville Se BASIS OF PRE-CAMBRIAN CORRELATION 13 series were deposited on some floor, although this floor has remained undiscovered up to the present time. Either the Laurentian gneiss, or some part of it, represents the original floor, subsequently melted and intruded into the overlying sediments, or the original floor remains unrecognized among the enormous bodies of intrusive rocks which resemble it in character. Resting on this Laurentian complex, in the region of the Great: Lakes, although penetrated by it, the lowest sedimentary series here recognized is the Keewatin series, a great body of rocks largely of pyroclastic origin, but in some districts containing great thicknesses of epiclastic material. It is not necessary here to make further reference to this great series which has been so well described by so many writers. In this region it is the oldest sedimentary rock recognizable as such. In the region of the St. Lawrence Valley this Keewatin is not seen, but there is a series of extraordinary thickness and enormous areal extent composed essentially of limestones, which rocks are practically absent in the Keewatin. Whether this series, known as the Grenville series, is the equivalent of the Keewatin is unknown as yet. If it be, the designation of the Keewatin by Van Hise as a series composed essentially of pyroclastic material to which stratigraphic methods cannot be applied and the assumption that such material characterized the earliest stratified deposits of the earth’s history, must be aban- doned, for the Grenville series is distinctly stratified and is one of the greatest limestones series in the earth’s crust. However that may be, these two series constitute the oldest sediments in the earth’s crust recognizable as such in their respective districts. Similar rocks apparently characterize extensive areas in the more northern and remote portions of Laurentia representing the oldest recognizable sediments in these districts. At the close of this first period of long-continued sedimentation there came an epoch of diastrophism—a thrust exerted from a south- easterly direction against the ancient continent threw these series into a succession of great folds running approximately parallel to the present valley of the St. Lawrence. Enormous bodies of granitic magma rose in great bathyliths along the axes of the folds, disinte- grating, fraying out, metamorphosing and partially absorbing the 14 FRANK D. ADAMS lower surfaces of the invaded sediments. Everywhere over thousands of square miles these ancient sedimentary rocks can be seen to have floated on the granite magma or to have been sunk into it and to have been cut to pieces by apophyses of it. That these movements were, in many cases at least, very slow, is shown by the fact that a study of the primary gneissic structure displayed by the bathyliths demonstrates that the upward movement of the latter began before crystallization had set in and continued while the magma was slowly filling with the products of crystallization and until it finally froze into a solid rock. This epoch of diastrophism, resulting in the elevation of great tracts of country, brings to a close the first clearly recognizable chapter in the history of Laurentia. After prolonged and profound denudation the sea again transgressed upon the continent of Laurentia and in this sea were laid down the strata of the earlier Huronian time. ‘The sea at this time passed over what is now the region of the Great Lakes and extended at least as far north as Lake Mistassini and as far west of the head of Lake Winnipeg. Locally it evidently extended as far inland as the latitude of the northern end of Hudson Bay. Within this earlier Huronian time there was, following the deposition of the Lower Huronian, a period of subordinate elevation and depression in the district of the Great Lakes marked by the deposition of the Middle Huronian. At the clese of this period of deposition, there was again an epoch of widely extended diastrophism due to a thrust exerted upon the south- ern portion of the continent from the ocean bed to the southeast and resulting in the widespread folding of the sediments which had been deposited over the southern portion of the protaxis, into a series of mountain ranges running in a northeasterly to southwesterly direction, with accompanying metamorphism of the folded strata and deep- seated intrusion of vast amounts of igneous rock. It may be that the great body of sediments forming the Grenville series really belongs to this rather than to the earlier Keewatin period, but be that as it may, these great orogenic movements which took place at the close of the earlier (Lower and Middle) Huronian time, brought to a close the second great chapter in the pre-Cambrian history of Laurentia. There then followed a period of deep and long-continued erosion, during which the Lower and Middle Huronian and the underlying BASIS OF PRE-CAMBRIAN CORRELATION 15 sedimentaries were swept away over the greater part of the region, leaving only the lower portion of the folds—the roots of the mountains —in the form of long narrow belts, separated by the granitic rocks marking the axes of the intervening anticlinal uplifts. This period of profound erosion constitutes what Lawson has termed the Eparchean Interval. Up to this time the movements which affected the continent of Laurentia were due, as has been stated, to thrusts coming from the southeast and caused by the negative element underlying the Paleozoic plain in this direction, at that time con- stituting the ocean bed, by its subsidence crowding against the posi- tive element which formed the continent of Laurentia. This is seen, as has been stated, in the distribution of the older rocks of the first two chapters of the pre-Cambrian in the form of long narrow belts running in a general northeasterly and southwesterly direction and representing the downward sagging portions of the ancient folds. Succeeding this long period of intense and widespread erosion, which followed upon the conclusion of Middle Huronian or pre- Animikie time, there was again a very widespread transgression of the sea upon the surface of the continent of Laurentia. In this was laid down a series of sediments which while occurring at localities sometimes separated from one another by hundreds of miles, yet preserve the same general features. These younger rocks form chains of islands fringing the east coast of Hudson Bay over a distance of about three hundred miles and have been described under the title of the Nastapoka series. This assemblage of beds dips toward Hudson Bay, generally at low angles, and lies in long parallel ridges with steep eastern faces. The strata comprise a group of arkoses and sandstones overlain by sandstones, argillites, cherty limestones and dolomites and calcareous shales with great intrusive sheets of diabase. The series has been found in places to have a thickness of at least three thousand feet and is further characterized by the occurrence at certain horizons of beds of banded jaspilite and iron ores. In the interior of Labrador, where the series dips at low angles toward the Atlantic, there is throughout a zone at least three hundred miles long, a development of similar rocks and here again occur the jaspilite beds. On the Atlantic side, at the head of Hamilton inlet, and further up the river of the same name, occurs a similar series, 16 FRANK D. ADAMS while on the Atlantic shores, far north, is found a great group present- ing many like features. West of James Bay and south of Hudson Bay, rocks lithologically like the Nastapoka series underlie a hilly district rising like an island above the surrounding flat-lying Paleozoic beds. In this great district of the pre-Cambrian west of Hudson Bay, large areas bordering the Arctic about the mouth of the Copper- mine River, and extending to Great Bear Lake, are underlain by a development of rocks resembling in nearly all respects the Nastapoka series and similar rocks have been described from the region about Great Slave Lake. In all these widely separated localities great developments of the same rocks occur and often are accompanied by beds of jaspilite and iron ore. Everywhere the members present the same general arrangement, the strata cut by many faults, dipping at comparatively low angles and forming ridges frequently capped by diabase, while in most cases the beds have been found overlying with a most striking unconformity older granitic and gneissic rocks. ‘These points of similarity seem to indicate that the scattered groups are all of about the same age and belong to a pre-Cambrian series probably at one time nearly continuous over the northern regions from the shores of the north Atlantic to about the valley of the Mackenzie. In Labra- dor and in the districts west of Hudson Bay the evidence indicates that the Nastapoka series was deposited after an epoch of severe erosion. Lake Mistassini, in northern Quebec, lies in a basin-like depression occupied by nearly flat-lying beds of cherty dolomite representing a portion of the Nastapoka series, while south of the lake these rocks have been found almost in contact with a develop- ment of the Lower (or Middle) Huronian, differing in no essential features from this group of rocks as found in numerous localities further southwest toward Lake Superior. The Lower Huronian is in a highly disturbed condition and has been penetrated by large bodies of granite. Neither the disturbances nor the granitic intrusions have affected the near-lying Nastapoka series so that the latter seems to be undoubtedly of post-Lower (or Middle) Huronian age, to have been formed after the Lower Huronian had been folded and invaded by the granites and then deeply eroded. ‘The relation of the two series resembles that existing between the Animikie and Lower Huro- BASIS OF PRE-CAMBRIAN CORRELATION iy) nian at Port Arthur, and largely on these grounds the Animikie or Upper Huronian of the Lake Superior region and the Nastapoka series of Labrador and the territories south and west of Hudson Bay been have considered to be equivalent to one another. The Nastapoka-Animikie series, forming the third major division of the pre-Cambrian in Laurentia, is of great importance, marking as it does one of the most widespread periods of submergence and depression in pre-Cambrian times, involving almost the whole con- tinent of Laurentia. No division of the pre-Cambrian in Laurentia is exposed over such a great area of country. ‘The positive move- ment which raised these rocks out of the sea was chiefly epeirogenic in character, for over the greater part of this area they still lie nearly flat. That the close of this time was, like those which preceded it, marked by an epoch of diastrophism, is shown by the widespread develop- ment of faults, accompanied in places by overthrusting. These are the superficial expression of the movements of deepseated intrusions, representing the last period of pre-Cambrian orogenic action. These post-Animikie granitic intrusions are to be seen on the east coast of Hudson Bay where, while the Nastapoka series in most places lies unconformably on the ancient Laurentian and the associated gneisses and schists, yet at some points it is cut by granitic intrusions. This epoch of mild diastrophism brought to a close the third great period in the pre-Cambrian history of Laurentia. The Nastapoka series seems to be the youngest division of the pre-Cambrian now found in the region east of Hudson Bay, but west of this inland sea, in a district bordering the southern shores of Lake Athabasca and stretching over an area of perhaps 24,000 square miles, is a great development of coarse sandstone in thick beds which along the shores of the lake aggregate at least four hundred feet in thickness. These, the Athabasca sandstones, lie in nearly horizontal positions, at times with a conglomerate layer at their base composed of fragments of the Laurentian granites and gneisses on which they rest with a strong unconformity. The Athabasca sandstones, or a very similar series, are exposed for a long distance up the valley which is continued seaward by Chesterfield Inlet, situated far north on the western shores of Hudson Bay. Between Lake Athabasca and the above locality, and in places associated with similar sandstones, are extensive areas 18 FRANK D. ADAMS underlain by basic and acid volcanics, porphyrites, and porphyries. These sandstones and volcanic rocks are, by the Canadian survey, classed provisionally as of pre-Cambrian age and it seems not improb- able that they are later than the groups of rocks about Great Bear and Great Slave Lakes which have been correlated with the Nastapoka series. Thus it is possible that the Athabasca sandstones and asso- ciated volcanics are the northern representatives of the Keweenawan of Lake Superior, concerning whose pre-Cambrian age there is a similar doubt. These sandstones are composed chiefly of quartz grains which it has been supposed have been largely derived from a series of quartzites known as the Marble Island quartzites and which on the western shores of Hudson Bay occur at intervals over a stretch of about one hundred and twenty miles. These are associated with masses of dark schists, etc., lying in a disturbed condition. The presence of siliceous material in the widespread Athabasca series, so like that composing the quartzites, would seem to indicate that these latter were at one time also widely developed. What their equivalents elsewhere are, if they have any, is not yet known. They apparently are older than both the Athabasca and the Nastapoka series and may belong to some division corresponding to the earlier Huronian. The rocks of the Athabasca-Keweenawan series are unaltered and lie practically flat. They have not been affected by orogenic dis- turbances or deep-seated plutonic intrusions. The uplift which raised them from the waters of the ocean was epeirogenic in character. Since the close of the pre-Cambrian, the continent of Laurentia, while preserving its character as a positive element, has undergone many oscillations, but orogenic or mountain-making forces have never manifested themselves, and the successive epeirogenic uplifts have resulted in and to a certain extent been compensated by the deep and long-continued erosion to which the continent has been subjected throughout the greater part of post-Proterozoic time. Using therefore the epochs of diastrophism, which mark the suc- cessive stages in the pre-Cambrian development of the continent, as a basis of correlation, provisionally grouping the Athabasca Sand- stones with the Nastapoka series, it would appear that we have three BASIS OF PRE-CAMBRIAN CORRELATION 19 major periods in the pre-Cambrian history of Laurentia separated by two critical epochs of diastrophism, with possibly a fourth period represented by the Laurentian rocks at the base of the series. That is to say we have three major periods in the pre-Cambrian succes- sion separated by epochs of diastrophism, which diastrophism at each epoch exhausted itself for the time. These are as follows: { Keweenawan-Athabasca INGO=EroterozolGe 44.) es ( Upper Huronian or Animikie-Nastapoka \ Middle Huronian Meso-Proterozoic........... - ( Lower Huronian Keewatin ( : | (Intrusi tact) : ) CIntrusive contac said OnE RUIS MZ vod og doo ss ) Laurentian (embracing the original crust, if | any remains) The lines drawn between the several subdivisions indicate unconformities, the heavier lines indicating the major breaks referred to in the text. If we attempt to make a comparative study of the earlier conti- nental evolution of North America and that of Asia, we note at the outset that the Siberian nucleus is a portion of that northern Polar region which comprises also Russia, Greenland, and Laurentia, against which stress has been continuously exerted by the denser masses of the more southern latitudes. As has been emphasized by Suess, the Siberian nucleus has been undisturbed since a pre- Cambrian date, and the same is essentially true of Laurentia also. We find that in Asia there were in geological time great mediterranea which, after they had been made the basins for the accumulation of great thicknesses of sediment, were successively closed by great thrusts from the south which folded up the sediments into mountain ranges and then converted these into dry land. In Europe the Alpine region was a marine strait in Cretaceous time, which was subsequently converted in this way into a mountain range. In the North American continent, of which Laurentia forms a part, there seems to have been a somewhat similar sequence in con- tinental development. Thus the Appalachian Mountains and the Cordilleran range of British Columbia represent ancient marine val- leys or straits whose sediments are now folded into series of mountain 20 FRANK D. ADAMS ranges. The thrusts which closed up these mediterranea and developed mountain ranges from them, were exerted in a northeasterly direction against the southwestern part of the continent, and in a northwesterly direction against the southeastern border of the continent, so that the folds are parallel to the margin of the present continent of Laurentia. Jf we inquire whether similar long, narrow, belt- like mediterranea existed in Laurentia in pre-Cambrian times, the answer seems to be in the negative. The surface of the con- tinent seems rather to have had upon it at intervals throughout geological time a succession of large, irregular-shaped bodies of water, somewhat resembling the present Hudson’s Bay, in which, however, great thicknesses of sediment were accumulated. The sediments deposited in these bodies of water in Keewatin, Grenville, and the Earlier Huronian times, were folded up into moun- tain ranges crossing the southern portion of the protaxis in a north- easterly and southwesterly direction, coinciding with the course of the Appalachian folding. The intense diastrophism which brought to a close the Eo-Protero- zoic and again the Meso-Proterozoic time was exerted apparently as far north as the middle of Labrador and the southern portion of Hudson’s Bay. In the later pre-Cambrian mediterranea the Nastapoka-Animikie series and the Athabasca-Keweenawan series were deposited. The almost entire absence of orogenic movement at the close of this time, combined with the great extent and comparatively unaltered character of the rocks, makes the break at the base of the Nastapoka-Animikie series probably the most pronounced in the whole pre-Cambrian succession in Laurentia. Thousands of square miles of practically flat-lying sediments overlie remnants of a highly folded and meta- morphosed antecedent series. We thus have two major breaks in the pre-Cambrian succession, each marked by an epoch of diastrophism which exhausted itself for the time. An identical series of two major breaks in the Proterozoic suc- cession, marked by epochs of pronounced diastrophism which in each case exhausted itself, is found in the Asiatic portion of the nucleus. BASIS OF PRE-CAMBRIAN CORRELATION 21 The succession here is as follows:! Neo-Proterozoic...... 1 Tung-yu limestone Slates, limestones (Hu-t’o system)... ./. T’ou-t’sun slates and quartzite. Meso-Proterozoic..... / Si-t’ai series Chiefly chlorite schist; quartzite conglomerate at the base. Siliceous marble, jasper, quartz- Se ea (Wu-t’ai system)...... Nan-t’ai series ite, and schist. Mica schists, gneiss, magnetite Shi-toui series quartize, and basal feldspathic quartzite. Bo-ProteroZzoic .... 5... T’ai-shan complex Basal complex of varied gneisses and younger intrusions. The lowest of these series, the T’ai-shan, resembles the Keewatin penetrated by Laurentian intrusions, being a metamorphic complex, the constituents of which are largely igneous, though perhaps in part sedimentary in origin.? This was brought to a close by a period of intense diastrophism. Suceeding this: We distinguish with great certainty a great thickness of very early Proterozoic sediments—the Wu-t’ai—which were intensely deformed and metamorphosed during a mid-Proterozoic epoch of orogeny, owing to pressure exerted by the outlying negative elements, and a later Proterozoic series—the Hu-t’o—which represents shore conditions and which was moderately deformed by pressure exerted by the same cause at the close of the Proterozoic. Applying therefore this criterion of diastrophic epochs to the correlation of the Proterozoic succession of these widely separated portions of the great northern nucleus, we obtain an identical result in both cases—the diastrophic movements seem to have affected the nucleus as a whole. It would seem that these diastrophic epochs designate certain of the unconformities in the succession both in the Siberian portion of the nucleus and in Laurentia, as major, dominant, and of special importance, and others as subordinate and of minor importance. We thus have indicated a division of the Proterozoic into EKo-, Meso- and Neo-Proterozoic. On this basis of correlation the T’ai-shan corresponds to the Keewatin-Laurentian complex; the Mu-t’ai to the Lower and Middle Huronian, and the Hu-t’o to the Animikie- Nastapoka series. t Research in China, Vol. Il, p. 4. alibede, Volek kartly) pro: 22 FRANK D. ADAMS These major breaks would seem to be as well marked and as impor- tant as those which characterize the separation of the Eo-Paleozoic and the Neo-Paleozoic in eastern America, or perhaps as that which brings to a close the Paleozoic succession in Europe. If, as our knowledge of the pre-Cambrian becomes more complete, the correlation of these rocks over great areas by a time relation to diastrophic epochs proves to be generally applicable, we have a basis of correlation of great value and importance. This will constitute a great advance as compared with our present methods, which afford no adequate means of determining the relative values of unconformi- ties and thus the successions in the most distant parts of the world are now being matched with each other and an unwarranted satis- faction is manifested if the number of unconformities in the pre-Cam- brian succession in different continents is approximately identical, and a sure and certain hope that all will prove to be satisfactory is expressed if there is no agreement. All that we really know at present is that there are great sequences of pre-Cambrian sedimentary formations, separated by many gaps from each other, which give one picture, growing less distinct in outline the farther back one goes, of the remotest periods of geological history, or, in other words, of periods of the earth’s pre-historic age which is, according to the author’s opinion, probably of greater length than all subsequent geological time.t It is believed, however, that through the recognition of these diastro- phic epochs, the dominant outlines of these pictures may perhaps be more clearly brought out and the relative values of the different parts thrown into relief in the case of each individual positive element, and that these epochs which have marked the successive stages of advance in Paleozoic and Mesozoic times, may thus be employed with advantage in deciphering the history of the pre-Cambrian as well. DISCUSSION CHARLES R. VAN HISE It is with pleasure that I discuss briefly Dr. Adams’ paper, since, allowing for differences of terminology, I find him in nearly complete accord with the tJ. J. Sederholm, Explanatory Notes to Accompany a Geological Sketch Map of Fenno-Scandinavia, Helsingfors, 1908, p. 31. BASIS OF PRE-CAMBRIAN CORRELATION 23 United States geologists in reference to the succession and relation of the pre- Cambrian series of Canada. So far as there are differences they will appear below. The elucidation of the pre-Cambrian succession for the Lake Superior region, which term as here used includes the great tract extending from the Lake of the Woods to north of Lake Huron and south to the Paleozoic rocks, has been the work of many men extending through many years. In 1892, when Bulletin 56 of the United States Geological Survey, on the Archean and Algonkian, appeared, the Lake Superior succession, as now recognized, had been fully worked out," with the exception that what was then called the Lower Huronian has since been found to comprise two series; also the series now called Keewatin was called Mareniscan, but was properly defined. Some years after the publication of this bulletin, Mr. A. E. Seaman discovered the unconformity mentioned in the lower Huronian of the Marquette district. As soon as this discovery was made it was appreciated that the two divisions of the Huronian in the original Huronian area worked out by Pumpelly, Leith, and myself correspond with the two divisions in the Marquette district. The classification of the pre-Cambrian as thus devel- oped was fully accepted by the International Geological Committee in 1904, and the table giving the succession was published by Leith in 1904, and by the com- mittee in 1905, as follows:? CAMBRIAN Upper sandstones, etc., of Lake Superior Unconformity PRE-CAMBRIAN Keweenawan (Nipigon) Unconformity Upper (Animikie) Unconformity Huronian ( Middle Unconformity Lower Unconformity Keewatin Eruptive contact Laurentian This succession is repeated by Dr. Adams in his communication, except that the unconformities are omitted, and it is extended to the entire Canadian pre- Cambrian region. It is indeed gratifying to have completely accepted for the great Canadian pre-Cambrian area the succession which has been worked out for the Lake Superior region, but Dr. Adams implies that his classification rests upon a sounder basis than the same classification offered by others since “drawing evidence from the area as a whole rather than from a few restricted areas on its southern border.” But unhappily for the contention of Dr. Adams, it is still true that the Lake Superior region is the only very extensive area in which the detailed geology has 1C. R. Van Hise, ‘Archean and Algonkian,”’ Bull. 86, U. S. G. S., p. 195. 2 Journal of Geology, Vol. XIII, p. 104. 24 FRANK D. ADAMS been worked out and the full succession given in the table has yet been found. Also when the succession was originally worked out all available information in reference to Canada as a whole was considered and it was suggested that within the regions about Hudson Bay and the Copper Mines Rivers, the equivalents of at least two divisions of the Huronian and of the Keweenawan appeared to be present.* As to the question of a fioor for the Keewatin, according to our view, the Keewatin is simply the most ancient series which has been discovered to the present time. Naturally being the oldest series discovered, we have not yet found the rocks upon which it was laid down, and we make no assumption in this matter. Dr. Adams speaks of the Keewatin as a sedimentary series. If he means by this that it is a series laid down at the surface, this characterization is correct. However, we have frequently pointed out that this series is essentially composed of igneous rocks, including both lavas and fragmentals, and is only very subordinately of ordinary sediments. As to the position of the Grenville series, I hold my opinion in reserve. Miller and Knight have shown that in the Hastings district where the series which Adams places in the Grenville is most extensively developed, there is an uncon- formity in the sediments. It is their belief that the greater part of the Hastings sediments, including the great limestone of Adams, belongs above this uncon- formity, below which is the Keewatin. If they are correct in this view, the larger part of the Hastings series included in Adams’ Grenville belongs not with the Keewatin but with the Lower or Middle Huronian. Dr. Adams says in reference to correlation by diastrophism: ‘‘This will con- stitute a great advance as compared with our present methods, which afford no adequate means of determining the relative values of unconformities, and thus the successions in the most distant parts of the world are now being matched with each other and an unwarranted satisfaction is manifested if the number of uncon- formities in the pre-Cambrian succession in different continents is approximately identical, and a sure and certain hope that all will prove to be satisfactory is expressed if there is no agreement.” In my address before the Geological Society of America a year ago, I intro- duced the table of pre-Cambrian series for China with their separated uncon- formities as given by Willis. I remarked that the Lake Superior Algonkian series in their number and their separating unconformities present a remarkable similarity to the Algonkian of China, but said it would “not be well to too strongly emphasize the close correlation suggested.”” Also I mentioned the “‘possibility that in the future we may be able to correlate the unconformable series of the Algonkian in provinces separated as far from one another as the Lake Superior region and Northern China.’’? ™ Charles R. Van Hise, Bull. 86, U. S. G. S., pp. 496-502, 1892; 16th Annual Report, U.S. G. S., Part I, pp. 807-9, 1896. 2 “The Problem of the pre-Cambrian,” Bull. Geol. Soc. of Am., Vol. XIX, p. 29. BASIS OF PRE-CAMBRIAN CORRELATION 25 Dr. Adams in his paper repeats the quotation from Willis and makes an identical suggestion as to correlation, but implies that this is done upon the basis of diastrophism. Evidently he thinks that there is an ‘“‘unwarranted satisfac- tion” in the first case and not in the second. Each unconformity between any two series of the Canadian region or of China means that between their depositions there has been an epoch of dias- trophism and one of erosion. I should be interested to know how the extents and the magnitudes of pre-Cambrian diastrophisms are to be determined except by studying the extents and magnitudes of the unconformities, that is, the extent and amount of the foldings, metamorphisms, erosions, etc., which intervened between the various series. In the paper which I have just read I pointed out that some unconformities are local, some regional, and some probably inter- continental. Adams points out that diastrophism may be regional or intercon- tinental. Is the distinction between the two greater than difference in language ? One we may suggest talks English, the other Esperanto. Evidently if satis- faction is unwarranted in one case it is unwarranted in the other. I am obliged to dissent altogether from the reasoning in Dr. Adams’ paper which makes discriminations as to the magnitudes of the various breaks, upon the basis of Willis’ hypothesis of positive and negative continental elements, and upon assumptions as to the sources of the thrusts. Even if these theories be assumed to be correct we do not know that they apply to the North American pre-Cambrian region, for we know nothing of the extent and distribution of the various pre-Cambrian series which are hidden under later rocks. In the western United States where extensive areas of pre-Cambrian protrude through the later rocks, and also in the Mississippi Valley, where are isolated areas of pre-Cambrian, several pre-Cambrian series occur, some of which are probably the equivalent of the series found in the Lake Superior region. Evidently the various pre-Cam- brian diastrophic movements cannot be assumed to be limited to the surface areas of pre-Cambrian. The question of the major groupings of the pre-Cambrian series I shall not attempt to go into in detail, since to do this would result in leaving less emphatic the reality of the accord as to the pre-Cambrian succession which has now come about and which I trust has come to stay between the Canadian and United States geologists, through the acceptance for Canada of the succession mainly worked out in a great area along the southern border of the pre-Cambrian region. However, I may recall that I fully discussed the major classification of the pre-Cambrian in my presidential address before the Geological Society a year ago, and gave reasons for the primary divisions of the pre-Cambrian into the Archean and Algonkian. In that address I gave objections to a zoic classifica- tion, similar to but not identical with that which Dr. Adams adheres to. His proposed major classification is eo-proterozoic, meso-proterozoic, and_neo- proterozoic. These terms imply that the pre-Cambrian had three distinctive life periods, an eo, a meso, and a neo. This may be the case, but until fossils.are 26 FRANK D. ADAMS found in the pre-Cambrian in sufficient abundance to justify a zoic classification, there can be no sufficient warrant for proposing that the major divisions of the pre-Cambrian be made upon a zoic basis. CLOSING DISCUSSION BY THE AUTHOR The aim of the paper on ‘‘The Basis of Pre-Cambrian Correlation” was, as stated, to suggest a method by which it might be found possible to correlate the various subdivisions of the pre-Cambrian rocks over widely extended areas rather than to enter upon a discussion of the classification of the pre-Cambrian of North America. With regard to this latter classification, however, it must be pointed out that the paper shows that in a general way the classification adopted by the Inter- national Committees (United States and Canada) on the “‘ Correlation of the Pre- Cambrian Rocks of the Lake Superior Region” and on the “‘ Pre-Cambrian Rocks of the Adirondack Mountains, the Original Laurentian Area of Canada and Eastern Ontario,” probably forms a satisfactory basis upon which the classifica- tion of the whole expanse of the great pre-Cambrian development of the Lauren- tian protaxis can be founded. Professor Van Hise is mistaken in stating that in the paper under discussion the succession recognized by these committees was adopted but that the unconformities were omitted, for in the wall diagram used to illustrate the paper, and upon which the succession of the pre-Cambrian rocks in Laurentia and China was set forth, the unconformities were especially indicated, black lines being used to show those which were of minor importance while broad red lines appropriately emphasized the major breaks in the succes- sion. The unconformities and their relative importance are also shown in the text ofthe paper. In fact, this is the crucial point of the paper so far as Laurentia is concerned. Professor Van Hise has insisted, in a long series of papers, that in the pre- Cambrian succession of North America there is one break which in importance far transcends all others, namely, that at the close of the Keewatin. Professor Law- son, however, has insisted that in this succession the chief break lies at quite a different horizon, namely, at the base of the Animikie. : The International Committees, while recognizing the succession of the various elements of the pre-Cambrian, absolutely declined to commit themselves to any opinion as to the relative magnitude or importance of the several unconformities which they recognized. A study of all the work—much of it recent—which has been done in the more northern portion of Canada indicates that Professor Lawson’s break—the Epar- chaean Interval as he terms it—is one of the greatest unconformities in the whole pre-Cambrian succession of Laurentia, and probably quite as important, if not more so, than the break at the close of the Keewatin, and that the pre-Cambrian rocks are represented, not by two great systems entirely distinct and separated from one another, but by three great systems. a BASIS OF PRE-CAMBRIAN CORRELATION 27 In Professor Van Hise’s presidential address he has referred to the succession of the pre-Cambrian rocks in Scotland, Finland, and China as determined by Geikie, Sederholm, and Bailey Willis, respectively, and notwithstanding the fact that in these successions from one to six unconformities exist, he has in each case selected one unconformity as of paramount importance, and correlating this with the break at the summit of the Keewatin in North America, has held that these various successions support a dual division of the pre-Cambrian rocks which he has maintained to be world-wide. He closes his address as follows: “I wish to express my firm belief that the dual division of the pre-Cambrian into two great groups of rocks [Archaean and Algonkian] seems now as firmly established as the division between any other two groups.”’ I feel, as stated in the paper, that in this conclusion an ‘‘unwarranted satisfaction” is expressed. To sum up, therefore, it seems that the division of the pre-Cambrian rocks of Laurentia into two great major divisions—Archaean and Algonkian—is not supported by the facts in our possession. The pre-Cambrian succession is apparently rather threefold, which three divisions may, for convenience, best be designated as Lower, Middle, and Upper (Eo- Meso- Neo-) Proterozoic, quite independent of any consideration of the presence or absence of life. CHAPTER sii EVOLUTION OF EARLY PALEOZOIC FAUNAS IN RELATION TO THEIR ENVIRONMENT CHARLES D. WALCOTT CONTENTS Introduction. North American Continent at the Beginning and at the Close of Cambrian Time. Life at the Beginning of Known Cambrian Time. Distribution of the Lower Cambrian (Olenellus) Fauna over the North American Continental Platform of Cambrian Time. Conditions in Middle and Upper Cambrian Time. Evolution of Faunas. INTRODUCTION The evolution of early Paleozoic faunas could be treated with far greater effectiveness 1f the studies now in progress on the Cambrian faunas were nearer completion. That of the brachiopods is well advanced? but the great collections of the U. S. National Museum, representing the crustacea and other invertebrates, have not been studied as to their mode of occurrence, geographic distribution, and biologic and environmental relations. Only a brief summary of the known evidence afforded by the Cambrian rocks and faunas of North America is considered in this paper. Animals and plants, as now known, are profoundly influenced by their environment, hence we will first broadly outline the conditions under which the known marine organisms of Cambrian time lived.’ NORTH AMERICAN CONTINENT AT THE BEGINNING AND AT THE CLOSE OF CAMBRIAN TIME The information obtained since the publication of my first map on this subject in 18913 has been assembled on the two accompanying maps by Mr. Bailey Willis. The first map outlines a central mass t Smithsonian Miscellaneous Collections, Vol. LIII, No. 4, 1908, pp. 139-65. 2 Bull. Geol. Soc. Amer., Vol. X, 1899, pp. 199-244. 3 Bull. U. S. Geol. Survey, No. 81, 1891, Pl. III. 28 EVOLUTION OF EARLY PALEOZOIC FAUNAS 29 of pre-Cambrian land, flanked on either side by large barrier islands that served to protect straits, sounds, or seas from the open ocean. Ocean currents flowed through the sounds with varying force and volume, not only from the cold arctic waters to the north, but from the warm tropical region to the south. The relative position of land and sea is based on the present interpretation of the observed characters and distribution of the pre-Cambrian and Lower Cambrian rocks. The distribution of Lower Cambrian faunas indicates the prob- able courses of the marine currents. A fundamental assumption is that the great ocean basins and continental masses occupied their present relative positions during at least the Algonkian portion of pre-Cambrian time. The map of the continent at the close of Cambrian time shows that during this period upon the continental area marked changes in the positions of the land and sea took place. Broad shallow seas followed the transgressing shore-line of Middle Cambrian time, offering most favorable conditions for the long-continued development and distribu- tion of marine life.t There were undoubtedly deep and shallow seas and bays, cold and warm waters, strong and weak ocean currents of unlike temperatures, protected bays with sandy and muddy bottoms, shore lines gently sloping to deep water, and many conditions promot- ing the evolution of the faunas through favorable or unfavorable changes in environment, temperature, and food-supply. The sediments of Cambrian time are mainly those deposited near the shore-line and in adjacent relatively shallow waters. There is little if anything to indicate deposits of the abyssal sea. If the littoral fauna of the Cambrian sea had begun to work its way down the conti- nental slopes beyond the continental margin into the depths, we can find no evidence of it, either in the Cambrian rocks, or in the character of the present deep-sea fauna. The life of Lower Cambrian time included Crustaceans (trilobites, ostracods), Mollusca (gasteropods), Molluscoidea (brachiopods), Vermes (annelids), Echinodermata (cystoids), Coelenterata (sponges, corals, jelly-fishes), and the simplest animals, the Protozoa (rhizopods). Immense quantities of microscopic, unicellular plants were undoubt- t See theoretic section at the close of Cambrian time: Bull. U. S. Geol. Survey, No. 81, 1891, Pl. II. 30 CHARLES DD" WALECOLT edly present, and, together with the minute Protozoa, must have formed the primary food-supply.' The réle assigned by Dr. W. K. Brooks to microscopic forms was an important factor in Cambrian time, for the organisms found in the rocks of that period were mainly carnivorous, and were adapted either to straining minute organisms from the water, or to gathering them up from the bottom. Uniform marine physical conditions over the submerged portions of the continental platform in Lower Cambrian time are indicated by the uniformity of the fauna on opposite sides of the present continent. Whether this fauna was distributed between the east and the west to the north of the central land-area, or south of it, is not definitely deter- mined, yet the absence of Lower Cambrian rocks and fossils from the collections made in the Arctic region, and the presence of closely allied species in the Lower Cambrian rocks of Alabama and California, point to the southern coast-line as the probable highway for the distribution of the littoral fauna. Nothing that suggests the Lower Cambrian fauna is known from South America; in this case, deep water may have been the barrier. With the advent of Middle Cambrian time land-areas came into existence on the northeast, forming barriers which so affected marine conditions in relation to life that the Paradoxides fauna developed in the Atlantic basin and the Olenoides fauna in the Appalachian region south of the Champlain Valley. To the south and on all sides of the central land-area the advancing seas forced the faunas to shift their habitat and either to adjust themselves to the new conditions or to perish. Local isolation for long periods led to the development of new forms, and these, when the barriers were removed, contested and com- peted for their position and life with other faunas until, by a process of elimination of those least fit to survive, there was hastened the devel- opment of a large and varied fauna. With the close of Middle Cam- brian time more stable conditions returned, and the era of rapid evolution was checked until the impulse of new conditions of environ- « W. K. Brooks, Studies from the Biological Laboratory, Johns Hopkins University, Vol. V, 1893, pp. 136-38. On p. 137 Dr. Brooks says: ‘‘The simplicity and abun- dance of the microscopic forms and their importance in the economy of nature show that the organic world has gradually shaped itself around and has been controlled by them.” — EVOLUTION OF EARLY PALEOZOIC FAUNAS ee. ment and an accumulated tendency to change resulted in the great evolution of life in the lower Ordovician. LIFE AT THE BEGINNING OF KNOWN CAMBRIAN TIME The traces of pre-Cambrian life, though very meager, are sufficient to indicate that the development of life was well advanced long before Cambrian time began. The characteristic fossil of the known pre- Cambrian fauna is Beltina danaz,* a crustacean probably more highly organized than the trilobite. The associated annelid trails indicate that this phase of the fauna was also strongly developed. Strati- graphically, this fragment of what must have been a large fauna occurs over 9,000 feet beneath an unconformity at the base of the upper por- tion of the Lower Cambrian in northern Montana.” This fact indicates that it is practically hopeless to search for the first forms of life—those that could leave a trace of their existence—in strata now referred to the Cambrian or early Paleozoic. With this thought in mind we shall consider what is known of the life of early Lower Cambrian (Georgian) time. The oldest known Cambrian fossils are found deep down in the Lower Cambrian strata of southwestern Nevada and the adjoining Inyo County area of eastern California. In sections 120 miles apart the Lower Cambrian has a thickness of over 5,000 feet, with a great limestone forming the upper 700 to 2,000 feet. Below this limestone calcareous strata occur, but the predominating rocks are sandstones, and arenaceous, siliceous, and calcareous shales. In the lower 400 feet of the Waucoba Springs section and the Barrel Spring section south of Silver Peak in western Nevada; the fauna includes: Annelid trails Trematobolus excelsis Walcott® Protopharetra, sp. undt. Obolella, sp. undt. Archaeocyathus, sp. undt. Orthotheca, sp. undt. Ethmophyllum cf. whitneyt Meek+ Holmia rowet, new species Mickwitzia occidens Walcotts Nevadia weeksi, new species t Bull. Geol. Soc. Amer., Vol. X, 1899, pp. 238, 239. 2C. D. Walcott, Observations vf 1908. 3 Walcott, Smithsonian Miscellaneous Collections, Vol. LIII, No. 5, 1908, pp. 185-89. 4 See Bull. U. S. Geol. Survey, No. 30, 1886, pp. 81-84. 5 Smithsonian Miscellaneous Collections, Vol. LIII, No. 3, 1908, p. 143. 6 [bid., p. 146. 32 CHARLES D. WALCOTT Although this fauna, according to our present knowledge, is the oldest known Cambrian fauna, it includes representatives of the several classes of invertebrates which I will enumerate. Actinozoa.—The corals are represented by a very primitive form of Protopharetra, a small form of cup-shaped Archaeocyathus, and a small Ethmophyllum closely allied if not identical with Ethmophyllum whitneyt (Meek),* which occurs higher in the section. The latter is not a notably simple or primitive form of the Archaeocyathinae; on the contrary, it is nearly as far advanced as any species known in the Cambrian. Vermes.—The annelid borings and trails that occur in and on the sandstones and shales are much like those of the Middle and Upper Cambrian. Molluscoidea.—The two species of brachiopods represent widely separated genera. Mickwitzia occidens Walcott? is one of the primi- tive forms of the Paterinidae, while Tvematobolus excelsis Walcott? is a typical form of the Siphonotretidae. The interval represented by the relative development of Mickwitzia and Trematobolus is sufficient to convince us that we must look far back in Cambrian, or it may be pre- Cambrian, time for the progenitors of the inarticulate brachiopods. Pteropoda.—The forms representing Orthotheca are abundant, large, strong, and evidently as well developed as those of the Middle Cambrian. Crustaceans.—The trilobites thus far found at this horizon are confined to one species of the genus Holmia. Nevadia weeksi, new species (referred at first to Holmia), has many segments, and is more primitive than such forms as Olenellus thompsoni Hall4 and Holmia bréggert (Walcott)5 of the upper portions of the Lower Cambrian section. The other species, Holmia rowei, new species, is of the same general type as Holmia bréggeri. The absence of all other trilobite genera is the most marked feature of this early Cambrian fauna. t E. gracile is considered to bea synonym of £. whitneyi (Bull. U. S. Geol. Survey, No. 30, 1886, pp. 81-84). 2 Smithsonian Miscellaneous Collections, Vol. LIII, No. 3, 1908, p. 143. 3 [bid., p. 146. 4 See Bull. U. S. Geol. Survey, No. 30, 1886, p. 167. 5 See Tenth Annual Report, U. S. Geol. Survey, 1891, p. 638. EVOLUTION OF EARLY PALEOZOIC FAUNAS 33 In the section roo miles to the south, at Resting Springs, Inyo County, California, a brachiopod closely related to Billingsella high- landensis Walcottt occurs 2,800 feet below the upper limestone, in association with the trilobite Holmia rowet. Comparing the species in the early Lower Cambrian fauna with the Olenellus fauna, in strata 5,000 feet higher in the section, we find a marked advance in the variety of the later fauna, but we do not know how much of this may be due to the absence, from our collections, of genera and species that may have existed during the deposition of the earlier sediments. In the earlier fauna of the Waucoba section the class characters of the Arthropoda, Mollusca, Molluscoidea, Vermes, and Coelenterata were developed, and while the study of the genera and species adds a little more to our knowledge of the rate of convergence backward in geologic time of the lines representing the evolution of animal life, it, at the same time, proves that a very long time-interval elapsed between the beginnings of life and the epoch represented by the Olenellus fauna.? DISTRIBUTION OF THE LOWER CAMBRIAN (OLENELLUS) FAUNA OVER THE NORTH AMERICAN CONTINENTAL PLATFORM OF CAMBRIAN TIME The Olenellus fauna lived on the eastern and western sides of a continent that rudely outlined, in its general configuration, the North American continent of today. Strictly speaking the fauna did not live upon the outer shore facing the ocean, but on the shores of interior seas, sounds, straits, or lagoons that occupied the intervals between the several land-masses that rose from the partly submerged conti- nental platform east and west of the central continental area. On the eastern side, the first land east of the central portion of the continent extended from Alabama northeast along the line of the present Appa- lachian range to and including the Green Mountains of Vermont. Whether or not the fauna existed in the Connecticut River region to the east of the Green Mountains is unknown. That it occurred further east is shown by its presence in eastern Massachusetts and northwestern Newfoundland. Its presence in a still more easterly t Proc. U. S. National Museum, Vol. XXVIII, 1905, p. 237. 2 Tenth Annual Report, U. S. Geol. Survey, 1891, p. 595. 34 CHARLES DD: WALCOLT, basin is proved by its occurrence on the peninsula of Avalon, to the east of the area of Archean rocks crossing central Newfoundland. It is not my intention to discuss the evidence upon which the asser- tion of the presence of these various outlying seas, sounds, etc., is based. The evidence of the existence of such bodies of water has been well presented by Dana.t What I wish to call attention to now is that the Olenellus fauna lived upon the eastern and western sides of the main North American continental area of late Algonkian and early Cambrian time. This view is sustained by the following observations: (1) The strata containing the Olenellus fauna are known only in the eastern and western portions of the continent; (2) as far as known the Lower Cambrian strata are absent in the interior of the continent; (3) the Upper Cambrian strata are unconformably superjacent to the Algonkian and Archean rocks over the areas where the Middle and Lower Cambrian formations are absent: (4) the strata of the Middle and Lower Cambrian are comformably beneath the Upper Cambrian on the eastern and western sides of the present continent in all sections where the three divisions are present.? The oldest known portion of the Olenellus fauna is limited to that section of the Cordilleran area mentioned on p. 197. This fauna was undoubtedly present on the continental shelves to the north and south, and may have been distributed around the southern extremity of the central land-area to the Hudson and Champlain valley region. Future investigation may thus prove that the Holmia asaphoides faunas of eastern New York is the oldest part of the Olenellus fauna upon the eastern side of the continent, and that it may be compared with the Holmia rowei fauna of the Cordilleran area. The presence in both localities of genera belonging to the Archaeocyathinae indi- cates that warm currents were passing through the straits or sounds to the east and west of the central continental areas, and that condi- t “Areas of Continental Progress in North America, and the Influence of the Conditions of These Areas on the Work Carried Forward within Them.” Bull. Geol. Soc. Amer., Vol. 1, 1889, pp. 36-48. ‘“‘ Archean Axes of Eastern North America,” Am. Jour. Sci., 3d ser., Vol. XX XIX, 1890, pp. 378-83. 2 The matter contained in the two preceding paragraphs appeared under the head- ng ‘‘ Habitat of the Olenellus Fauna” in the Tenth Annual Report, U. S. Geol. Survey, 1891, Pp. 556, 557- : 3 Tenth Annual Report, U. S. Geol. Survey. 1891, p. 570. etter eats een EVOLUTION OF EARLY PALEOZOIC FAUNAS 35 tions were favorable for a varied fauna. The arenaceous beds (with ripple-marks and trails) of the western Nevada-California area and the interformational conglomerates of eastern New York prove the presence in both areas of relatively shallow water. The Olenellus thompsoni fauna,‘ of late Lower Cambrian time, is widely distributed about the margins of the continental area. Begin- ning at the Straits of Belle Isle on the northeast, it has been found in eastern Massachusetts, western Vermont, eastern New York, eastern Pennsylvania, and along the Appalachian area as far south as central Alabama. In the Cordilleran area it is known to extend from Inyo County, California, to the Wasatch Mountains of Utah, and north- ward to the line of the Canadian Pacific Railway in British Columbia. With the exception of vertebrates, echinoderms, and cephalopods, the class-characters of the early Lower Cambrian fauna of Nevada were well advanced toward the varied and rich fauna of the lower Ordo- vician. CONDITIONS DURING MIDDLE AND UPPER CAMBRIAN TIME The physical conditions of the late Lower Cambrian time continued into early Middle Cambrian time, followed during Middle Cambrian time by a gradual submergence through erosion and probable warping of the surface of most of the continental area south of the Great Lake region.?, As the marine waters slowly encroached upon this great area and upon the shores adjoining the Appalachian and Cordilleran seas the marine life of the times met with conditions favorable to a large development. This is illustrated by the abundant and varied Paradoxides fauna on the Atlantic side and the equally varied Pacific basin Olenoides? fauna found in nearly all localities where the Middle Cambrian sediments were deposited. t Ibid., p. 560. 2 Am. Jour. Sct., Vol. XLIV, 1892, pp. 56, 57- 3 The Olenoides fauna is found on both the eastern and western sides of the northern Pacific Ocean, and the Paradoxides fauna on both sides of the northern Atlantic Ocean. This fauna includes a group of trilobites that are represented more or less fully in the Middle Cambrian rocks of North America, east of the Atlantic basin Paradoxides faunas, and in eastern Asia. The fauna includes: Olenoides Meek, Dorypyge Dames, Neolenus Matthew, Dorypygella Walcott, Damesella Walcott, Blachwelderia Walcott, Zacanthoides Walcott, and Kootenia Walcott. 36 CHARLES. DA WALCOTT EVOLUTION OF FAUNAS That the environment of the faunas of Middle Cambrian time was more favorable for their rapid evolution than that of Lower and Upper Cambrian time is strikingly shown by the stratigraphic distribution of the brachiopods. In the restricted waters of Lower Cambrian time the known brachiopods (of the entire world) were represented by 20 genera and 75 species. In the expanding seas of Middle Cambrian time 31 genera and 243 species are known to have existed. With the more uniform conditions of Upper Cambrian time, and the dying-out of the impulse to variation created by both favorable and unfavorable environments in Middle Cambrian time, the brachiopods decreased in variety and numbers, and are represented by only 23 genera and 137 species. About the same relative numerical ratios are exhibited by the trilobites but the exact statistics are not yet available. The favorable environment of the Middle Cambrian fauna is well illustrated by the development of Ogygopsis, Asaphiscus, and Bathyuriscus of Cordil- leran Middle Cambrian time,’ genera which are so far in advance of contemporary trilobitic genera that they have sometimes been referred, upon biological grounds, to the Upper Cambrian.? The closing of Cambrian time was accompanied and followed by changes in the relations of the sea and land upon the continental plat- form that were favorable, like those of Middle Cambrian time, to the evolution of new genera and species, and to the existence of multitudes of individuals of the prolific species. This is not the place for a detailed discussion of the faunas and sediments of the lower Paleozoic. Only the broadest generalizations can be touched upon. I think, however, that sufficient has been said to fix in your minds the following conclusions: (1) That more or less uniform and favorable, even warm, climatic conditions must be appealed to in explanation of the widespread occurrence of almost identical coral-like organisms in the Lower Cambrian, and of the vast number of individuals of various species of trilobites, etc., which existed in Middle Cambrian time; (2) that the rapid and accentuated devel- t See Bull. U. S. Geol. Survey, No. 30, 1886, Pls. XXX, XXXI, and Canadian Alpine Journal, Vol. I, No. 2, 1908, Pl. 3. 2G. F. Matthew, Trans. Roy. Soc., Canada, 2d ser., Vol. V, 1899, p. 64. EVOLUTION OF EARLY PALEOZOIC FAUNAS By opment of the Middle Cambrian faunas was due in great measure to enlarged opportunity caused by the extension of the Cambrian seas and the consequent shifting of shore-lines and changes in habitat, etc.; (3) that the diversification of the Middle Cambrian fauna, as a whole, may have been due, in a large degree, to the rapid development of narrowly provincial or isolated faunas that were subsequently merged into the more widely distributed fauna by the breaking-down of the restrictive barriers; and (4) that a free and more or less complete interchange of currents in the Cambrian seas was strongly instrumental in producing those cosmopolitan faunas so characteristic of the early Paleozoic. In other words it is evident that the evolution of the early Paleozoic faunas was profoundly influenced by their environment. Nore.—Since this paper was written in November, 1908, I have made a detailed examination of the genera and species referred to the Mesonacidae (Smithsonian Miscellaneous Collections, Vol. LIII, No. 6, 1910) and referred Holmia meeksi of the original paper to the genus Nevadia and limited its range to the basal Lower Cambrian fossiliferous strata in Nevada. The Holmia rowet fauna (p. 31) is now closely limited in stratigraphic range and is below the Archaeocyathinae-bearing strata. May, 1910 PALEOGEOGRAPHIC MAPS OF NORTH AMERICA? tr AND 2. EARLY CAMBRIAN AND LATE CAMBRIAN?2 BAILEY WILLIS U. S. Geological Survey At the Baltimore Meeting of the American Association for the Advancement of Science a number of paleogeographic maps of North America, representing the continent at intervals from Cam- brian to Quaternary, were exhibited. They had been prepared in collaboration with some of the geologists who presented papers in the symposium on correlation, and to a certain extent they serve to illustrate the changing geologic conditions which form a factor in the problems of correlation. I have been requested to publish them in connection with the correlation papers in the Journal of Geology, and am glad to do so, although it is not practicable to present a discussion of the particular facts which have been considered in the construction of each individual map. In general the lines of evidence have been considered somewhat in the following manner. A certain period having been selected as that which should be mapped, the epicontinental strata pertaining to that time interval have been delineated. The phenomena of sedimentation and erosion have then been correlated, with a view to determining the sources of sediment and topographic conditions of land areas, and from these data the probable positions of lands have been more or less definitely inferred. ‘Thus, certain areas within the continental margin are distinguished as land or sea, and these areas may be defined as separate bodies or connected according to inferences based upon isolated occurrences or upon later effects of erosion. It is assumed that the great oceanic basins and such deeps as the Gulf of Mexico and the Caribbean have been permanent features of the earth’s surface at least since some time in the pre-Cambrian. These deeps can thus be placed upon the map and their connection with the epicontinental seas may be tentatively established. « Published by permission of the Director of the U. S. Geological Survey. 2 Based largely on data furnished by C. D. Walcott. 38 a PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 39 When the distribution of lands and waters is thus inferentially completed, we may infer further that the dominant features of oceanic circulation have obeyed the conditions of atmospheric cir- culation and of rotation of the sphere which now govern the great oceanic eddies. We may introduce in the Atlantic and Pacific the dominant drifts from east to west in equatorial regions with the resulting circulation northward along the east coast and southward along the west coast of the continent. A circulation of the oceanic waters in the epicontinental seas must result from the great oceanic drifts, and the direction of flow will be determined by the configura- tion of the lands and the depths of the seas. From the geographic conditions thus developed inferences regard- ing the climate and the life habitats of the time may be drawn. If now we turn to the records of paleontology and compare the dis- tribution of faunas and floras with the conditions of distribution which should result from the inferred physical phenomena, we may check the whole line of reasoning and by a readjustment draw a step nearer to the truth. This is the method which has been pursued in making the maps of North America that are published with the papers in this number and that will appear in connection with further papers of the series. In a first essay of this kind (and I am not aware of any earlier attempt to combine the various lines of evidence in a similar manner) it is probable that important facts have been overlooked. The very broad scope of the discussion makes this probability almost a certainty, and it is not to be expected that the maps here presented should give a final or satisfactory solution of the problems. They are to be regarded as tentative and suggestive only. On one point they have been particularly criticized, it being said that each individual map covers so long a period of time and such diverse conditions that they do not truly represent any special geo- graphic phase of the continent. This criticism is valid, and one of the steps in the advancement of knowledge will be that of selecting narrower time limits and more precise correlations than have been attempted in these cases. We may undoubtedly make progress in this direction at the present time so that the fifteen maps which will accompany this series may be replaced by two or three times as 4O0 BAILEY WILLIS WHYOOY | LOWER C eI W114 Gy ~~ NORTH AMERICA YZ% 470% bese OO —_ wo uniles ——s LEGEND OCEANIC BASINS . | MARINE WATERS (EPICONTINENTAL) SEA OR LAND, MORE LIKELY SEA LAND OR SEA, MORE LIKELY LAND ‘LANDS INDETERMINATE AREAS POLAR EQUATORIAL —————> no S OS MARINE CURRENTS 120° PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 41 many; but there is danger in carrying the refinements too far on the basis of paleontologic correlation alone, since it is still difficult to distinguish between synchronous and homotaxial faunas or floras. It may be hoped that these paleogeographic studies will themselves assist us to a better understanding of the evolution of life conditions and thus lead to a solution of some of the problems of correlation with the aid of biologic evidence. I. LOWER CAMBRIAN NORTH AMERICA The map of lower Cambrian North America presented herewith conforms to the outline developed by Mr. Walcott in the course of his studies. East and west of the central land mass are relatively narrow sounds limited on the oceanic side by islands or land masses of indeterminate extent. The old land area of Appalachia is believed to have covered the region of the West Indian Islands, it being well established that a somewhat extensive land extended to the southeast of the Appalachian trough, and it being plausible that that land lay between the Atlantic deep on the northeast and the deeps of the Caribbean and Gulf of Mexico. In the adaptation of marine cur- rents to oceanic and continental features, it is inferred that the return waters from the Arctic occupied the sounds along the inner continental margins. The distribution of these currents suggests that the habitat of the lower Cambrian fauna of the Appalachian trough on the east and the British Columbia-Nevada trough on the west was determined by the cool waters flowing southward. This view of dispersion of the faunas from the north is not shared by Mr. Walcott, who presents the alternative hypothesis of a connection of the faunas around the southern margin of the continent. The fauna of the Nevada basin appears to belong to warmer waters than that of British Columbia, inasmuch as it contains corals. The land areas of lower Cambrian time throughout the northern hemisphere appear to have been large. ‘There is evidence in the character of the sediments and in glacial deposits in China that there were marked contrasts of climate. 2. LATE MIDDLE AND UPPER CAMBRIAN NORTH AMERICA The map of late middle and upper Cambrian North America represents an expansion of the area of the epicontinental sea which BAILEY WIELIS 42 G (Uy, te, gi %, LAS ZN ip ETN — SS pe 5 SSS rR = 5 z AS a) ~ = Z fa SSS WS ec SECRK\ \ s ees WAG SY NON WQS BE ASS AS \ (ae | : RNR. a iz a < -) = 4 1S) ° NE WATERS (EPICONTINENTAL) MARI SEA OR LAND, MORE LIKELY SEA LAND OR EA, MORE LIKELY LAND Ss 1) LANDS S INDETERMINATE AREA POLAR EQUATORIAL E CURRENTS MARIN 110° Toor PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 43 probably was not at any time actually reached. The middle Cam- brian sea extended further in certain areas than the upper Cambrian and retreated while the upper Cambrian sea spread over other regions. These details are not well worked out, though in part recognized. The map truly presents, however, the general fact that North America was to a great extent submerged and the land areas very markedly reduced. The prevailingly fine and calcareous sediments of the wide seas and the siliceous coastal plain sediments of the littoral deposits indicate that the relief of the land was low. The conditions of marine circulation had apparently been modified by the expansion of the interior sea, and the climate conditions incident to widespread seas and low lands had become so ameliorated that similar habitats prevailed throughout a very wide range of latitude. CHAPTER WV PHYSICAL AND FAUNAL EVOLUTION OF NORTH AMERICA DURING ORDOVICIC, SILURIC, AND EARLY DEVONIC TIME AMADEUS W. GRABAU Columbia University The following classification of the Ordovicic! and Siluric has recently been published by the author and will be made the basis of the present discussion of these systems :? Upper Siluric or Monroan. Middle Siluric or Salinan. . Lower Siluric or Niagaran. Upper Ordovicic or Trentonian. Middle Ordovicic or Chazyan. Lower Ordovicic or Beekmantownian. eo eee le) Nears) A. THE LOWER ORDOVICIC OR BEEKMANTOWNIAN At the beginning of Ordovicic time, as now generally recognized, the great marine transgression or positive diastrophic movement, which obtained throughout Upper Cambric time, was in progress, so that the early Beekmantown strata overlapped the Upper Cambric (Saratogan) and came to rest directly upon the crystalline basement. The basal portion of the sedimentary series is generally quartz sandstone of greater or less purity, or sometimes a conglomerate with crystalline pebbles of local origin. This basal sandstone is commonly referred to the ‘‘ Potsdam,” that term being used synony- mously with Upper Cambric. Aside from the question as to whether or not the Potsdam sandstone of the type locality is really of Upper Cambric age, it must of course be apparent that in a normally over- lapping series of strata deposited by a transgressing sea, the basal sand member would naturally rise in the series in the direction of transgression and overlap, and that hence a basal sand is not every- where of the same age. In northwestern New York, in Ontario, and in northern Michigan, these basal sands are probably in all cases 1 The editor does not approve the terms “ Ordovicic,”’ ‘‘ Siluric,”’ ete. 2 Science, N. S., Vol. XXIX, pp. 351-56, February, 19009. 44 45 TAY | WRRARY WG : ig GEOL oa er, L? £9 Zs Ve gata: > Sete S 3 Y QS SN SOs & Q/ . ARN AN BAY ay fe aN y Iw pews LSS P b (i aera aid PHVSICAL AND FAUNAL EVOLUTION Fig. 1.—Paleogeographic map of North America at end of Upper Cambric time, R. Peninsula of Rockymontana. and probable currents. 46 AMADEUS W. GRABAU post-Saratogan, belonging to the basal portion of the Beekmantown series as generally defined. This is clearly true of the conglomeritic layer at the base of the Little Falls dolomite in the Mohawk Valley, and is probably also true of the so-called Potsdam of the Black River region and the westward continuation of the outcrop in Canada. There is good reason for believing that the sea at the end of Saratogan time did not cover the present site of Lake Ontario, and that the basal sandstones of the Ontario region belong to the base of the over- lapping early Beekmantown. In some cases the basal sands (St. Mary’s sands) are even younger than this (Lowville, N. Y., Encamp- ment d’Ours, Isle Lacloche, etc.), for the immediately overlying strata carry late Chazy (Lowville) or even Black River fossils, and, so far as now known, there is no break in sedimentation between these basal sands and the beds immediately succeeding, which thus deter- mine their age. In all such cases, until positive evidence of a pro- nounced physical break or disconformity is determined between the two series, or until the basal bed is shown by unquestionable fossil evidence (exclusive of Scolithus, burrows, trails, and other problem- atic markings which may characterize various Paleozoic sand- stones) to be of Cambric age, logical reasoning compels us to regard the age of the basal sandstone in each case as essentially that of the fossiliferous beds immediately succeeding, unless these are the very lowest post-Cambric beds. One other point should be clearly emphasized. It is by no means established that the basal sandstones are everywhere of marine origin. In fact, the general absence of fossils, the frequent cross- bedding and other characters point rather to a continental origin of a part, at least, of this basal series, the agents of deposition being rivers or the wind. ‘There is scarcely a geologist today who is satisfied with the complacent explanation, current only a short time ago, that the absence of fossils in a sandstone is due to “ unfavorable conditions at the time of deposition,” or to subsequent destruction of the fossils, in some mysterious way or other. That fossils abound in marine sandstones of all kinds, and even in conglomerates, is a well-known fact, and that the sands along our modern. sea-shores are rich in shells and other hard parts of organisms, is equally a matter of common knowledge. The argument that the absence of fossils in a ee PHYSICAL AND FAUNAL EVOLUTION 47 rock which elsewhere carries them, indicates some peculiarity of the sea-shore at that point, capable of barring the life of the sea, is a laborious explanation to fit a preconceived notion of the origin of the formation in question. Nor must we forget that the North American continent was above the sea during long periods of pre-Cambric and Cambric time, and that on those vast land areas subaérial deposition as well as erosion must have been in progress. It is therefore to be expected that in many, if not in most, regions the Paleozoic series begins with a formation of continental origin, the upper portion of which was reworked by the transgressing sea, and became incor- porated as a basal member of the marine series succeeding. In this manner the contact between the continental and marine series often became an apparently conformable and perfectly gradational one, the hiatus between them being masked. It will of course be impossible in such a case to determine whether a basal bed of con- tinental origin is of pre-Cambric, of Cambric, or of post-Cambric age; all that can be determined is the period at which its upper portion was reworked by the transgressing sea. If the basal bed is of slight thickness it is in such a case best referred to the age of the immediately succeeding marine formation. The question naturally arises, should the lower portion of the Beekmantown be referred to the Cambric with which it forms a continuous transgressive series, or should it be retained in the Ordo- vicic with the remainder of the Beekmantown ? While in New York the fauna is, so far as known, an Ordovicic one, in other localities beds considered of the same age carry a mixed Cambric and Ordo- vicic fauna. In this respect these beds and the typical Saratogan, as well as the St. Croix series of Minnesota and Wisconsin, probably correspond to the Tremadocien of Europe, which is classed as Upper Cambric by British geologists, but by German and other continental geologists as basal Ordovicic (Unter Silur). Matthew correlates these beds with the Asaphellus homfrayi beds of the St. John section, and so places them above the Dictyonema flabellijorme beds, which at present are also included in the base of the Ordovicic by some continental geologists. That such transitional formations are to be expected in any complete depositional series is, of course, obvious, and their precise reference is a matter of secondary importance. AMADEUS W. GRABAU 48 NING 7 \N NWSW A, Mats NY x SRA fe sax NS \\ VW < Yost Ky - , NS VX RO RAY b r \ ee WY : » SS Fig. 2.—Paleogeographic map of North America in early Beekmantownian time, showing extent of maximum transgression and probable currents. PHYSICAL AND FAUNAL EVOLUTION 49 To make a distinct system of them, as has been proposed by some, will not solve the difficulty, because the transitional beds are likely to be of very variable quantitative and chronologic values in different localities. The accepted base of the Ordovicic—the summit of the Saratoga formation in New York, of the Franconia sandstone in the Mississippi Valley, and of the Asaphellus homjrayi beds on the Atlantic coast—is a perfectly satisfactory one, as long as the syn- chroneity of these formations is granted. (Compare Figs. 1 and 2.) REGRESSIONAL PHASE OF THE BEEKMANTOWN As has been fully demonstrated by the author elsewhere’ and by Berkey,” the chief event of Beekmantown time in North America was the widespread regressive movement of the sea and the re- emergence of the continent. The extent of the movement is shown by the extensive disconformity between the Beekmantown and ihe succeeding Chazy formations. From this it appears that only a narrow trough remained in the Appalachian region as the sole repre- sentative of the interior or Mississippian sea, while most of the Pacific coast region, west of the Rocky Mountains axis, was prob- ably uncovered (see map, Fig. 3). In the interior of North America the emergence was accompanied by widespread continental deposi- tion recorded in the St. Peter sandstone. The detailed character- istics of this formation; the all but complete absence of fossils; the cross-bedding shown in many exposures; the rounded character of the sand grains, their grooved and pitted surfaces; the absence of the finer impurities; the uniformity of the size of grain in the same region—all point to long-continued shifting about of these sands by winds, and testify against their marine origin. The inclusions in the quartz grains show them to be derived from the crystalline oldland, the chief source being probably the Canadian shield. In some cases the contact with the underlying formations is abrupt and disconformable, showing that erosion of the uncovered limestones preceded the deposition of the sands. Not infrequently the contact t A. W. Grabau, “Physical Characters and History of Some New York Forma- tions,” Science, N. S., Vol. XXII., pp. 528 ff., October, 1905; also, ‘Types of Sedi- mentary Overlap,”’ Bull. Geol. Soc. Amer., Vol. XVII, pp. 616 ff. aC. P. Berkey, ‘‘Paleogeography of St. Peter Time,” Bull. Geol. Soc. Amer., Vol. XVII, pp. 229-50. AMADEUS W. GRABAU 50 i TY NS | | | | | ‘ xy A ESS KWAN $ ROow AS 2 if “\ WN \S ! \ RS ! BW 4 K \ » x AW RQRY NS AW y aes SS i Vt \ \ SS Se AS) WY * AHS Fig. 3.—Paleogeographic map of North America at the end of Beekmantownian time, showing maximum retreat of the sea. = 3 os & PHYSICAL AND FAUNAL EVOLUTION 51 is as sharply marked as that of aeolian quartz sands found upon the clear-swept limestone floors of some modern deserts.'. In some cases, however, there appears to be absolute conformity between the St. Peter sandstone and the underlying dolomites, pointing to con- tinuous deposition. Both in Wisconsin and in Minnesota, the lower Magnesian beds are often slightly folded, and the lower St. Peter sandstone is likewise involved in these folds? (Fig. 4). The upper St. Peter, however, and the overlying Stones River, which are per- fectly conformable, are not involved in these folds. In Minne- sota, the Oneota, New Richmond, and Shakopee formations have a combined thickness of 1o5 to 260 feet. If the Jordan and St. Lawrence beds are regarded as Ordovicic, though they still contain Dicellocephalus, the thickness is increased to 190 feet minimum or 673 feet maximum. ‘The faunas of all the beds of the Lower Mag- hesian series indicate lowest Ordovicic and close relation- Fig. 4.—Showing the relationship of the 4 : Upper Stones River (S. R.) and lower Beek- ship to the Upper Cambric. mantown (B.) Beds of Minnesota and the In the Black River region, included St. Peter (St. P.) (Redrawn from Cushing records 20 to 60 Halland Sardeson.) feet of lowest Beekmantown (Theresa), succeeded disconform- ably by Upper Chazy (Pamelia and Lowville limestones). The base is probably not exposed in this section, the basal sandstone, called Potsdam by Cushing, being most likely of later age. In the Mohawk Valley, 350 feet of Beekmantown (Little Falls dolomite) is followed disconformably by Upper Chazy (Lowville); but here, too, the base of the Beekmantown is not shown, and hence the true thickness is unknown. In the Lake Champlain region the Beekman- town is 1,800 feet thick; in southern Pennsylvania 2,250 to 2,300 feet; in central Pennsylvania nearly 2,500 feet; and in the Arbuckle Moun- tains of Oklahoma 1,250 feet. In all these localities, except central Pennsylvania, the upper limit of the Beekmantown is marked by a dis- t Compare Zittel, Beitrége zur Geologie und Palaeontologie der lybischen Wiiste. 2 Hall and Sardeson, Bull. Geol. Soc. Amer., Vol. III., pp. 354, 355. 52 AMADEUS W. GRABAU conformity, and the highest beds are thus wanting. In Center County, Pennsylvania, the upper beds appear to be completely represented. They are succeeded by 2,335 feet of dolomitic limestones, classed by Collie with the Beekmantown, but for reasons given elsewhere! referred by the author to the Chazy; and by 235 feet of limestones of Upper Stones River (Upper Chazy) age. The succession seems to be uninter- rupted, placing this section in the region of non-emergence, while the others cited belong in that of emergence during late Beekmantown time. The section in central Pennsylvania does not, however, show the base of the Beekmantown, which is thus thicker than 2,500 feet (see Fig. 5). There seems no reason for doubting that the higher Mohawk Central Valley Penn. = = enter — ST L} = — = = ————— == ———— SSS ==S1] = ae Hiatus Fig. 5.—Diagram showing relationships between the Mokawk and Central Pennsylvania sections and the character of the overlaps and “‘off-laps,” with the pro- gressively decreasing hiatus. beds of the Beekmantown were progressively deposited during the slow retreat of the sea, and that each higher member had, in general, a smaller areal distribution than the preceding one. On this view the successive members have the ‘“off-lapping” arrangement of shingles, except that the earlier and lower formations are continuous beneath the higher ones. This is regressive overlap or “‘off-lap,” and seems to supply the only rational explanation answering to the facts. ‘To assume that the whole of the Beekmantown was deposited before retreat began, not only makes the negative diastrophic movement a cataclysmic one, where the positive movement was a very slow 1 Types of Sedimentary Overlap, p. 619. PHYSICAL AND FAUNAL EVOLUTION 53 and regular one, but also necessitates the further assumption of an enormous erosion during the succeeding transgressive movements, which not only removed the greater part of several thousand feet of strata over the northern United States area, but also the whole of the extensive Canadian deposits of Beekmantown which must have reached far toward the Arctic regions, if the entire Beekmantown was deposited as a transgressional series. Aside from the fact that erosion would scarcely be very active during a positive diastrophic movement or transgression of the sea, it can hardly be assumed that such exten- sive erosion preceded the deposition of the St. Peter sandstone and the Chazy formation. Moreover, the intimate relation between the Lower St. Peter and the underlying Lower Beekmantown demands a close succession in deposition, the lower sand beds being probably deposited by the shoaling sea itself. If that is indeed the case, no higher dolomites of Beekmantown age than are now found ever existed in the Minnesota area. West of the Rocky Mountains, the basal Uinta quartzite is chiefly if not wholly a continental deposit of pre-marine Cambric time, 12,000 feet or more in thickness. Upon this enormous basement series the eastward-transgressing Cambric sea laid down its progressively over- lapping strata, the upper beds of the series being reworked during the progress. The transgressing sea apparently did not reach the region of the eastern Uintas, where the basal quartzite is succeeded by the Lodore shales. From these shales Powell reported Carboniferous (Mississippic 2) fossils,t and he gives evidence of the existence of a disconformity between these shales and the basal sandstone. Weeks? identifies the Lodore with the Iron Creek shales of Berkey, which he between the Uinta and the so-called Ogden’ quartzites, and which Berkey correctly correlates with the Cambro-Ordovicic Ute limestone of the Wasatch. Weeks fails to recognize that, as Berkey has shown, the “‘Ogden”’ quartzite has united with the Uinta in the eastern section, the intervening shales having wedged out. The Lodore of the eastern Uintas thus lies above the ‘“‘Ogden”’ horizon, and corresponds to a part of the overlapping Mississippic series (see Fig. 6). The Lower Ordovicic retreat is shown in the western section by the 1 Geol. of the Uinta Mountains. 2? Bull. Geol. Soc. Amer., Vol. XVIII, pp. 435, 436. 3 Blackwelder has recently shown that the ““Ogden” of the Uintas is not the true Ogden. Mul ial Kt NN Ki i i a == Seoeeea ees = S— eee eeeeeeeeeeeeeeee Ss =a i = Sea 5eS—— es ee i Mi \ \ = = AMADEUS W. GRABAU W Uinta E Vinta Wasatch \ \ Fig. 6.—Diagram showing the relationships and overlaps of the Paleozoic strata west of the Rocky Mountains. appearance of the so-called Ogden quartzite and conglomerate, which bears internal evidence of continental, chiefly river, origin; and to all appearance represents the sand and gravel wash which followed the retreating sea westward, and which was probably in large part derived from the basal Uinta quartzites, with which the ‘Ogden”’ seems to become confluent in the east- ern Uintas.'. This quartzite rests on higher beds in the western sections than in the eastern, thus showing the same relationship to the underlying series that is exhibited by the St. Peter sandstone. In the _ western Uintas it is underlain by 1,200 feet of shales, regarded as Cambric, though the highest beds may represent the Lower Ordovicic. In the Wasatch Mountains the Ute limestone, 2,000 feet thick, and of Cambro-Ordovicic age, lies between the “Ogden” and Uinta quartzites. In the Eureka section of central Nevada, the Pogonip limestone, 2,700 feet thick, underlies the Eureka quartzite, the westward continuation of the Ogden. The Pogonip repre- sents, in its basal portion, the transi- tion beds from the Upper Cambric, but corresponds mostly to the Beek- mantown of eastern North America. Beneath it are 6,200 feet of fossiliferous shales and limestones of Cambric age. Here, as in the eastern region, succes- t Berkey, Bull. Geol. Soc. Amer., Vol. XVI, PP- 517—30- PHYSICAL AND FAUNAL EVOLUTION 55 sively higher beds appear beneath the quartzite in the direction of the retreat, indicating continuous deposition during the slow regressive movement of the sea, this being checked as the localities successively emerged. A widespread negative diastrophic movement is thus shown to have taken place over the whole of the North American continent, accompanied and followed by the spread of subaérial clastics over most of the area. At least 2,500 feet of calcareous strata were deposited in the non-emerging areas, and most of this constitutes the depositional equivalent of the retreatal movement (see map, Rg) The Beekmantown jfaunas.—The Beekmantown faunas are, so far, best known from the Lake Champlain region, the Mingen Islands, and the Newfoundland section. The Lake Champlain region, including the Phillipsburg section of the Canadian exten- sion, has furnished a considerable number of species. Its distinctive character will be seen on consulting published lists. The Pogonip limestone of Nevada contains mostly species un- known outside of this formation in the West, though a number of them have been referred by Walcott to eastern species, largely Tren- ton and Chazy types. In almost all such cases, however, the identi- fication is provisional, and regarded by Walcott himself as doubtful. There is nothing in the character of the fauna which positively demands its reference to either the Chazy or Trenton, as has been done. GRAPTOLITE FACIES OF THE BEEKMANTOWNIAN In the Hudson and St. Lawrence valleys the Beekmantown is represented by the lower portion of the Hudson River shales, above the beds with Dictyonema flabelliformis. Some 340 feet of strata appears to be referable to this series, of which the lower 300 feet constitutes the first and second Deepkill zones, synchronous with the Upper Point Levis zone of Canada and the St. Anne zone of New- foundland. Here the genera Chlonograptus, Goniograptus, Tetra- graptus, and Phyllograptus (P. anna), with Didymograptus bifidus, characterize a succession of zones recognizable in various parts of the world. The upper forty feet of this series (third Deepkill zone) 56 AMADEUS W. GRABAU is characterized by Diplograptus dentatus and Cry ptogra ptus antenna- rius. This zone has been correlated by Ruedemann with the Chazy limestones of the Champlain region, but it probably is also referable to the Beekmantown, since most of its characteristic types occur in the Upper Arenig of Great Britain. The world-wide distribution of these graptolite faunas suggests that they were dispersed by strong currents sweeping through an open channel along the inner or western side of an Appalachian continent and its New England extension (Taconia). The fauna was most likely spread from Australia by strong currents passing up the west coast of South America and entering the Appalachian synclinal trough, along which it flowed northeastward to Newfoundland. Northwestward of this zone of mud-deposition we find the limestone of the Beekmantown grading down, by the addition of quartz grains, into the basal quartz sand, without intervening mud deposits (see map, Fig. 2). With the progress of Beekmantown retreat the channel was closed, a land bridge connecting Taconia with Laurentia. Thus the mud deposition was checked and only a moderate thickness of Beekmantown strata of this type was formed. This represents, there- fore, largely the lower part of the Beekmantown. As has been stated, it is probable that the Chazy is unrepresented by deposits of mud, the channel remaining closed until the end of that period, when it reopened through the progress of Chazy transgression, and the Normanskill beds, with a late Chazy (Lowville) and Black River graptolite fauna, were formed. In spite of some similarities, the Diplograptus dentatus and the Coenograptus gracilis zones are quite distinct, the important genera, Odontocaulus, Thamnograptus, Corynoides, Azygograptus, Leptograptus, Nemagraptus (Coeno- graptus), Dicellograptus, and Dicranograptus, appearing suddenly. In like manner, the characteristic Beekmantown genera, Dendro- graptus, Goniograptus, Loganograptus, Dichograptus, Tetragraptus, Phyllograptus, and Didymograptus, continue through the third Deepkill zone, only the last: of them extending into the Normanskill zone. Certain long-lived genera, Desmograptus, Diplograptus, Clonograptus, Climacograptus, and Cryptograptus, begin in the third Deepkill zone and extend through all or most of the remaining Ordovicic. Of the genera in common between the third Deepkill and the Normanskill, PHYSICAL AND FAUNAL EVOLUTION 57 Didymograptus is represented by three species,’ all common in the Normanskill, and all distinct from those of the lower horizons, where eighteen species are recorded. Of the genera beginning in the third Deepkill, or Point Levis zone, Climacograptus has only one species in the lower zone, which is not known above that zone, while there are thirteen species, most of them abundant, in the Normanskill; Crypto- graptus has one species in the lower and two others in the higher zone, common in each case; Desmograptus has two species in the lower and one in the higher, the latter rare; Diplograptus has four species in the lower and thirteen in the higher horizon, all distinct; while Clonograptus has two rare species in the lower and nine in the upper, mostly common. It is thus seen that there are no species in common between the two zones, and the most characteristic genera of each are unknown or rare in the other. On the other hand, six out of the twenty-four species listed by Ruedemann for the third Deepkill zone, or 25 per cent., occur also in one or both of the lower zones. Its relationship to that and distinctness from the Norman- skill zone thus becomes evident. The forty feet of the third Deepkill zone probably represents the last deposits in an already shoaling and contracting channel before interruption took place, this break con- tinuing to the end of Chazy time, when a new graptolite fauna came into existence.? On the whole, the Beekmantown represents one of the large stratigraphic divisions of the Ordovicic of North America. Its fauna is essentially a unit, and although the succeeding Chazy fauna is in part, at least, derived from the Beekmantown, its distinctness is nevertheless marked. The Beekmantown corresponds to a great negative diastrophic movement, with the exception of the lower por- tion, and its thickness (2,500 feet where fully developed) shows that it represents fully one:third of the entire Ordovicic series, and pre- sumably represents one-third of Ordovicic time. From this it follows that the Beekmantown alone represents the Lower Ordovicic in North America, the Middle Ordovicic beginning with Chazy deposition. The term Beekmantownian has therefore been proposed as the North. American equivalent of Lower Ordovicic, while the t Varieties are here classed as species. 2 See Ruedemann, Graptolites of New York, Vols. I and II. 58 AMADEUS W. GRABAU term Canadian becomes obsolete. The Beekmantownian corresponds essentially to the Arenigian of England and its continental equivalent. B. THE MIDDLE ORDOVICIC OR CHAZYAN In its maximum development, the Chazy shows nearly 2,500 feet of limestones, many portions of which are highly fossiliferous. An apparently complete development of this series, resting with con- formity upon the Beekmantown, is described by Collie from Center County, Pennsylvania. Here 2,335 feet of dolomitic limestones, with fossils poorly preserved, succeeds the Upper Beekmantownian; and above this is 235 feet of fossiliferous limestones of Upper Stones River (Upper Chazy) age, succeeded in turn by the Black River. Sedimentation seems to have been continuous throughout, and this section may therefore be regarded as typical of the Mid-Ordovicic in its entirety. In southern Pennsylvania, Stose reports a discon- formity and hiatus between the Beekmantown and Chazy (Stones River) limestones. The latter are from 800 to 1,000 feet thick, and are succeeded by the Chambersburg limestone (100 to 600 feet thick), which carries an Upper Chazy and Black River fauna. Continuous deposition seems to have obtained between the two series. In the Lake Champlain region, a hiatus also exists between the Beekman- town and Chazy, with the result that only about goo feet of Chazy occurs in this region below the Black River beds. In western New- foundland at least 2,000 feet of strata is referable to this series, the succession being conformable. Here, however, the upper limit of the Chazy is not known, the highest bed (P) being succeeded by continental sediments of much later age. In the Arbuckle Mountains the hiatus between Beekmantown and Chazy is marked by a sandstone, and only the upper 2,000 feet of the Chazy (Simpson) is shown, followed by Black River. The Chazy is absent in the Mohawk Valley, except for a few feet of Lowville which lies disconformably upon the eroded surface of the Lower Beekmantown (Little Falls dolomite), and is conformably succeeded by the Black River. In the Black River Valley, at Water- town and northward, the sedimentation from Lowville to Black River is continuous and gradual. Cushing? finds in the Theresa quadrangle t Bull. Geol. Soc. Amer., Vol. XIX, pp. 155-76. PHYSICAL AND FAUNAL EVOLUTION 59 from 115 to 215 feet of strata beneath the Black River, and resting disconformably upon the Lower Beekmantown (Theresa formation), which, with its basal sandstone (called Potsdam by Cushing), has a maximum thickness of 140 feet. Cushing restricts the term Lowville to the upper 75 to 85 feet of pre-Black River strata, separating the lower part, on paleontologic grounds, as the Pamelia limestone. At Lowville and elsewhere this series overlaps the Beekmantown, resting with a basal sandstone upon the crystallines. The Pamelia fauna is an Upper Stones River fauna, according to Ulrich, while the fauna of the Lowville is compared with that of the Upper Chazy." In the Canadian region, only Upper Chazy (Lowville and pos- sibly the Pamelia equivalent) is present. In a number of localities it rests directly upon the pre-Cambrics, generally with a basal sand- stone (St. Mary’s sandstone). In some cases, however, lower beds (Beekmantown, with basal sands) have been reported. In Min- nesota and Wisconsin the Upper Chazy is called Stones River, though it represents only the upper part of the Stones River formation of Safford’s Tennessee section where the thickness is 360 feet. The Minnesota beds are 32 feet thick and are probably the exact equiva- lent of the Lowville of New York, though the fauna is stated to be more like that of the Pamelia. The relation of these beds to the underlying St. Peter sandstone is significant, since the contact is per fectly conformable and gradational. Moreover, Stones River fossils (Hormotoma gracilis, Lophospira perangulata, etc.) are found in some of the upper beds of the St. Peter, showing that with the advent of the Chazy sea, the sand dunes of the St. Peter desert were incorporated as basal sands in the overlying formation. This meant, of course, a slight reworking of the sands by the encroaching sea. That this reworking did not reach to the bottom of the St. Peter, at least not in all cases, is shown by the persistence of the folds and faults in the lower beds, whereas they are absent in the upper (see Fig. 4). A comparison of sections shows that in general lower beds of Chazy age appear progressively above the St. Peter as we proceed southward and eastward. The relationship of these beds to the St. Peter has not been discussed in detail, but it is certain that in some localities, at least, the gradation observed in Minnesota obtains. The relation- t See Cushing, Joc. cit. A . a GRABAU AMADEUS W. Rh tS ; 4 \ < 2 \ Mey = E INNS WL RTS WEY EE esas 9 \ UX EAS AS Ns ¥ ws NX WS Ni \ TAY A \: YS QRS 3 \ SSE SN AN \ SOS O a) Ne ‘ i tS S Wo vv SS \ Taconic Island. > 60 s WEES PRB os (site wea 7 LSPA oy HET |e Kk SEC ¢ j ii SS Pty) : Laie , A PVs Ax SS re A \ OWN Te \ ASS | Fig. 7.—Paleogeographic map at the end of Chazy time and the probable currents. M, Ozark Island, the remains of Mississippia; T. PHYSICAL AND FAUNAL EVOLUTION 61 ship is, accordingly, that of a progressively overlapping transgres- sional series to its basal bed, and this is the interpretation favored by all the sections. The Chazy was, in fact, characterized by a transgressive or positive diastrophic movement throughout (barring possible minor oscillations), and therefore only the higher beds are found in the region of late submergence. The thickness of the formation beneath the Black River, forms in general a reliable guide to the division of the Chazy represented, though of course there may be discovered some minor disconformities which would vitiate detailed correlations made on this basis in a given region. No unquestionable Chazy beds have been reported from the Pacific region, where the Trentonian seems to rest directly upon the Eureka quartzite in Nevada, and either Siluric or Devonic succeeds the Ogden quartzite of the Wasatch, with Mississippic beds succeeding the same in the Uintas. The west coast transgression was, therefore, less pronounced, the Nevada region remaining still uncovered at the end of Chazy time (see map, Fig. 7). If Chazy beds occur in the West, they must be sought for in western Nevada and California. It is, of course, impossible to say how much has been removed by late Ordovicic erosion. It is not improbable that the Chazy extended east of Eureka, Nev., but was removed again in Upper Ordovicic time. The Chazy fauna.—At the beginning of Chazy time, the Cham- plain gulf was entirely distinct from the Appalachian gulf, there being a land connection between the Laurentio-Mississippian con- tinent and the united Appalachia and Taconia, or Ancient New England continent (see map, Fig. 3). The faunas were thus to a large extent distinct, representing, in fact, the Atlantic and the southern type. The southern type was, in general, the Stones River type of fauna; the character of which may be seen by consulting published lists. The Atlantic type is seen in the fauna of the Champlain basin, which admits of a threefold division, a lower (Div. A) with Orthis costalis; a middle (Div. B) with Maclurea magna; and an upper (Div. C) with Camarotoechia plena. That these two types of faunas were not wholly distinct in middle and later Chazy time is shown by the occurrence of true Champlain species of Mid-Chazy age, including Maclurea magna in the middle 62 AMADEUS W. GRABAU portion of the “Stones River beds” of southern Pennsylvania; and of Upper Chazy species, including Camarotoechia plena, in the Cham- bersburg limestone of the same region. Whether this implies an Appalachian extension of the Champlain gulf or a connection with the Atlantic in the southern part of North America must be deter- mined by further detailed study. It is probably true, however, that the open passage along the west border of Appalachia and Taconia, through which the mud-bearing currents swept in early Beekmantown time, and which formed the route of dispersal for the graptolite fauna of that age, was not re-established until late Chazy or Black River time. This accounts for the slight development of the grap- tolite-bearing shales referable to the Chazy in the Hudson and Levis series. The disconformity which represents this interruption would probably be difficult to trace in strata of such similar lithic characters. THE BLACK RIVER FORMATION This formation is widespread, having been traced by its fauna from the Champlain Valley to the upper Mississippi and southward to Oklahoma and the Appalachians. Over this area it forms an excellent datum plane from which correlation of overlying and under- lying formations becomes possible. Its thickness is never very great; it is only 7 feet in the type region, at Watertown, N. Y., 50-60 feet in Minnesota, less than too feet in Oklahoma, go feet in southern Penn- sylvania, and 7o feet in the Champlain Valley. Faunally, it repre- sents a transition between the Chazy and Trenton, as will be seen by consulting published lists. Its classification with either the Chazy or the Trenton is therefore permissible. Since the formation represents the unchecked continuance of the transgressive movement initiated at the opening of Chazy time, its classification with that series of strata as Mid-Ordovicic is perhaps most desirable. THE NORMANSKILL BEDS AND FAUNA The Normanskill shales are generally regarded as representing the shale facies of the Lower or Middle Trenton. Ruedemann, in his recently published monograph parallels them with the Lowville, Black River, and Lower Trenton.t In Rysedorf Hill, the shale includes a conglomerate, the pebbles of which, regarded as nearly syn- t Graptolites of New York, Part II. ON Op ae ek mtg ea le la PHYSICAL AND FAUNAL EVOLUTION 63 chronous with the shale, carry a Lowville-Black River—Lower Trenton fauna, with some elements (Christiania trentonensis, Ampyx hastatus, Remopleurides, Sphaerocoryphe, Cybele, etc.) suggesting a geographic connection with the European sea of that time. The typical graptolite fauna of the Normanskill includes more than 60 species in all, though the widely distributed forms are much fewer. The more constant and characteristic species comprise: (1) Coeno- graptus (Nemagraptus) gracilis; (2) Dicellograptus sextans; (3) D. divaricatus; (4) Dicranograptus jurcatus; (5) D. ramosus; (6) Diplo- graptus foliaceous; (7) D. angustifolius; (8) Climacograptus parvus; and (9) C. bicornis. Of this list, Nos. 1, 2, 4, and 8 are the most characteristic index fossils of this zone. Didymograptus sagitticaults, Gurley, and Climacograptus scharenbergii, Lapw, may also be men- tioned as characteristic though less widely distributed forms. Besides the numerous localities along the Hudson and St. Law- rence valleys, this fauna is known from Maine and New Brunswick. In the Appalachian region it is definitely known only from New Jersey and from Bebb County, Alabama; it is also doubtfully identi- fied from western Virginia and eastern Tennessee. It has been found in Arkansas and the Ouachita Mountains of Oklahoma; in southern Nevada (Belmont and Letson peak); and in the Kicking Horse Pass of the Rocky Mountains of British Columbia. It is also known from New South Wales and Victoria in Australia; and from southern Scotland, Scania, and France. The distribution of this fauna is such as to suggest an eastern and a western land mass (Appalachia and Rockymontana) of low relief, with currents of the Gulf Stream type sweeping along their inner borders and distributing the graptolites, which became entombed in the muds that accumulated in these channels of moderate depth. The division of what was probably a single great current, sweeping north along the South American coast, and carrying the graptolites from Australia, was probably due to the existence of an Ozarkian island or Archipelago, along the borders of which, as in Arkansas and Oklahoma, were deposited some of these black muds. One arm of the divided current swept along the east coast of Rockymontana to the Arctic Sea of Alaska; the other along the west coast of Appa- lachia, past a Newfoundland island, and across the North Atlantic GRABAU AMADEUS W. << Ya \\) YS \ SY \ RN SS AU S NY Ws ‘ NI AIS ; j Fig. 8.—Paleogeographic map at the end of Trenton time, showing second maxi- The currents are indicated for Black River time. Normanskill graptolites. mum transgression in the Ordovicic. @ indicates distribution of PHYSICAL AND FAUNAL EVOLUTION 6 mn to northern Europe (see Fig. 8). Within the protected interior sea, limestones (Upper Stones River and Black River) accumulated. Limestones accumulated also along the shores of Laurentia (Canadian shield) in the St. Lawrence channel, the two types of sediment and faunas thus occurring side by side. There is no need for postulating a dividing ridge in this channel, for the faunas and sedimentation would remain different as long as the different physical conditions persisted. In Great Britain and elsewhere in Europe the zone of Coeno- graptus gracilis forms the summit of the Middle Ordovicic. The next succeeding zone (Hartfell shales of the Moffat district) is of Upper Ordovicic or Caradocian age. This begins with the zone of Dicranograptus clingani, which in North America is represented by the Magog shales or Diplograptus am plexicaulis zone, which succeeds the Normanskill beds. The diastrophic movement, which in North America resulted in the emergence of most of the continent at the end of Lower Ordo- vicic time, was likewise marked, though to a less extent, in Europe. Lamansky has recently shown’ that between Baltic Port and the banks of the river Volkov, the Lower Ordovicic beds (Etage B) show the progressive off-lapping structure characteristic of a retreatal or beveled-off series of sediments. At Baltic Port only the Mega- laspis planilimbata zone (BIla) occurs. Farther east, at Reval, the higher Asaphus bréggeri zone (BIIP) and a part of the Asaphus lepidurus zone (BIIy) have appeared. In the extreme east of the gouvernement of St. Petersburg, on the Volkov, the whole of BIIy, and the Asaphus expansus zone (BIIIa) have come in above the others. The line of disconformity and erosion is marked by slight irregularities, by glauconite, iron oxide, and phosphate concretions, rarely by siliceous sediments. Above the erosion plane, the beds of BIIIf and BIIIy (zones with Asaphus raniceps and Asaphus eichwaldi) show progressive overlapping, the latter being repre- sented only by clastic material at Baltic Port. Above these lies the Echinosphaerites limestone C, which shows continued westward overlapping. tW. Lamansky, ‘Die Altesten silurischen Schichten Russlands,” Mém. du Comité Geol., N. S., Livr. XX, 1905. 66 AMADEUS W. GRABAU The regressional movement here indicated appears to coincide with that of North America, but the transgressive movement seems to have begun somewhat earlier, unless the Lower Ordovicic is regarded as ending with the Asaphus expansus zone. C. THE UPPER ORDOVICIC OR TRENTONIAN Most current classifications of the Ordovicic formations of North America unite the Black River and Trenton limestones under Clarke and Schuchert’s term Mohawkian, which is made synonymous with Middle Ordovicic. As we have seen, the Middle Ordovicic is repre- sented by the Chazyan, which in its maximum development includes some 2,500 feet of limestone strata, and is therefore comparable in Buffalo Rochester = Lorraine 600 —<———— Bees = Ss ====== SZ = = = == = —{— SS == : I ——— SS SSS —— ==> z T = —————————— Sa KKK ren = I wa Sees bass —— = = = I I i We an —e === Bechmartown =r Fig. 9.—Diagram showing the relationships of the Ordovicic strata of New York between Saratoga and Buffalo. magnitude and, inferentially, in time value, to the Beekmantownian or Lower Ordovicic. The fauna of the Chazyan is, moreover, distinct from both preceding and succeeding faunas, and the natural dividing-line between the Middle and the Upper Ordovicic is shown, by paleontologic, stratigraphic, and diastrophic reasons, to be within or above the Black River horizon; .a division coinciding with that made in the European series. The Trenton limestone of America is not a stratigraphic unit, but, as has been repeatedly demonstrated by Ruedemann and noted by many observers, it is the limestone phase of a series which elsewhere is in part or mostly represented by Utica shale. In the Mohawk Valley the dividing-line between Utica and Trenton is a line constantly rising to the west, the transition being in some cases abrupt, though probably in most cases it is gradual. Ruedemann has pointed out the progressive increase in thickness PHYSICAL AND FAUNAL EVOLUTION 67 westward of the limestone, and corresponding decrease in the shale; the former increasing from 4o feet at Saratoga to 430 feet at Utica, and to 954 feet at Rochester, while the latter decreases from 1,260 feet to 710 feet to probably zero over the same localities (Fig. 9). In the South Mountain region of southern Pennsylvania, the Cham- bersburg limestone of Stones River, Black River, and Lower Trenton age is succeeded by 1,000 feet of gray fossiliferous and dark bituminous shales, with intercalated limestone members in the basal portion which carry a Lower Trenton fauna. The shales contain Le ptobolus insignis, Triarthrus becki, and Utica graptolites, and are succeeded by a sandstone with the fauna of the Eden beds of the Cincinnati region, formerly identified as Utica, but now regarded as younger than that formation. In central Pennsylvania, some 600 feet of Trenton succeeds to Black River, and is followed by 650 feet of Utica shale. In this zone also we have some typical Trenton species, such as Dalmanella testudinaria, Isoteles platycephalus, etc., associated with Triarthrus becki and other Utica species. The various sections clearly show that along the western border of the Appalachians, dark graptolite shales continued to form in Upper Ordovicic time, while westward from this the Trenton limestone represents the cal- careous phase of the Utica-Trenton series (see map, Fig. 8). THE TRENTON-UTICA GRAPTOLITE FAUNAS The Normanskill fauna is succeeded by that of the Magog shales or zone of Diplograptus amplexicaulis—the upper Dicellograptus zone of Gurley. This represents, according to Lapworth, highest Llandeilo or lowest Caradoc, and forms a transition to the true Utica fauna. Many of its species are characteristic of the Hartfell shales (Caradocian) of southern Scotland, though others are equally char- acteristic of the Normanskill and Glenkiln shales. Ruedemann re- gards this fauna as a relict of the preceding one. The Didymograptidae have vanished entirely, and the Dicranograptidae almost; only the long range forms, Dicranograptus ramosus and nicholsoni, are still observed, and the Diplograptidae . . . . hold now almost entirely the field, with the genera Diplograptus, Climacograptus, and Cryptograptus.* The fauna is best developed near Quebec and at the north end of Lake Memphremagog, only fragmentary representation occurring x Op: cit., I, 30. 68 AMADEUS W. GRABAU in New York. The fauna is rapidly changing, the true Upper Ordo- vicic faunas begin to appear, and soon the typical Utica fauna, with Glossograptus quadrimucronatus, Climacograptus typicalis, Cory- noides curtus, and, less frequently, Leptograptus flaccidus, Dicrano- graptus nicholsoni, and Climacograptus putillus is established. The association of typical Utica graptolites with characteristic Trenton limestone fossils, as Tvocholites ammonius, Cameroceras proteijorme, and Schizocrania filosa, bears on the previously discussed question of the synchroneity of the Utica and Trenton. Climacograptus typicalis, the typical Utica species, is reported by Winchell and Ulrich from the Fusispira and Nematopora beds of the middle Galena of Minnesota. Since the Galena of that section follows directly upon the Black River, this occurrence is only a short distance above the base of the Trenton, which is thus indicated to be the western limestone equivalent of the Utica shale of the east. As already noted Ruedemann has cited abundant evidence of the gradual westward extension of the successively higher zones of the Utica, and the replacement of the limestone phase (Trenton) by them. The Galena-Trenton limestone of the Lake Winnepeg region con- tains Dictyonema canadense (Whiteaves), Thamnograptus affinis (Whiteaves), and the typical Utica species, Climacogra ptus ty picalis (Hall). Whiteaves concludes that the Galena-Trenton of Lake Winnepeg ‘‘most probably represents the whole of the Utica and Trenton formations, inclusive of the Galena.””? THE CINCINNATI GROUP This is the upper calcareous phase of the latest Upper Ordovicic, and comprises, in ascending order, the Eden, Maysville, and Rich- mond. The Eden was formerly correlated with the Utica, but the underlying Trenton mainly represents that formation. The Eden is in part equivalent to the Frankfort shales, though the occurrence of Climacograptus typicalis in the Eden strata would favor its former correlation with the Utica. The Maysville represents later Lorraine as developed in New York, though the fauna, being that of a cal- careous facies, is markedly different. Ulrich has reported a disconformity at the base of the Eden, in the Cincinnati section, but this, if it exists, does not appear to be t Quoted by Ruedemann, op. cit., II, 28. PHYSICAL AND FAUNAL EVOLUTION 69 of great importance. It certainly does not represent Utica shale. There is, however, a marked and widespread disconformity between the Lower and Upper Trentonian, the late Richmond resting on Trenton or even earlier beds. This is observed throughout the Rocky Mountain area, the upper Mississippi region, and to a less extent in other sections. It signifies a retreat of the sea, probably at the end of Trenton time, and a return during late Richmond time. THE TRENTON-CINCINNATI FAUNAS While on the whole the faunas of the Trenton limestone and of each one of the three divisions of the Cincinnati group are sufficiently distinct, so that it is not difficult to recognize the exact horizon of each by a careful analysis of the fauna, there is, nevertheless, a unity in these faunas, which shows their unmistakable relationship to one another and their distinctness from the preceding faunas. It is this broad similarity of faunas, together with the distinctness from the preceding faunas, the intimate relation of the limestone to the Utica shale which it replaces, and the moderate thickness of the formation in its best development, as compared with that of the Chazy and Beekmantown, that has led me to place the Trenton limestone in the Upper Ordovicic. In England, the Upper Ordovicic or Caradocian (Bala) is characterized by the same faunal elements which here appear for the first time. The more common species characterizing the Upper Ordovicic from the Trenton up, and occurring in most if not all of its beds, include Rajfinesquina alternata, Plectambonites sericea, Dinorthis subquadrata, Plectorthis plicatella, Dalmanella testudinaria, Platystrophia biforata; Protowarthia cancellata, Lios pira micula, Clathrospira subconica, Trochonema umbilicatum, Camero- ceras proteijorme, Calymmene callice phala, Isoteles gigas, I. maximus, and Ceraurus pleurexanthemus. Some of these species begin in the Black River or even in the Upper Stones River, but they are most characteristic of the higher horizons. THE CONTINENTAL PHASE OF UPPER ORDOVICIC TIME The later epochs of Upper Ordovicic time were characterized by continental or non-marine sedimentation in the Appalachian region. The earliest of these is the conglomeratic and quartz-sand 7° AMADEUS W. GRABAU series found directly overlying the fossiliferous marine Ordovicic of southern Pennsylvania, and generally classed by Pennsylvania geologists as “‘Oneida.”’ This is a gray to white, rarely red, con- glomerate and quartz sandstone with rounded quartz pebbles and characterized by extensive cross-bedding. Its maximum thickness today is in Bald Eagle Mountain, near Tyrone City, Blair County, Pennsylvania, after which locality I originally named it.! This name, however, was preoccupied, and the formation under con- sideration is therefore called the Bald Eagle conglomerate, this ridge being due to the resistant character of this and the succeeding formation. At Tyrone the thickness is 1,319 feet, while thirty miles to the northeast, at the Bellefonte Gap, through the same ridge, the thickness is only 550 feet, and the formation is divisible into a lower hard gray sandstone without pebbles, 170 feet thick, and an upper greenish-gray somewhat ochery and micaceous sandstone with intercalated greenish shales. One hundred and sixty miles north- west from Tyrone, at Buffalo, this formation (Oswego sandstone) is 75 feet thick. It is here a white quartzite lying below the red Queenston shales, and represents only the upper layers of the gradually spreading fan of clastic sediments. In central New York the Oswego is 185 feet thick at the falls of the Salmon River. It there succeeds the Lorraine beds with perfect conformity, some Lorraine fossils extending into the lower Oswego. There can be little doubt that these beds represent the northern and western attenuated upper beds of the Bald Eagle conglomerate of Pennsylvania, unless indeed they belong to one or more distinct fans with a source in the north. The character of the rock, its cross-bedding, and absence of fossils indicate continental origin, and this is also shown by the nature of the overlap, which is that characteristic of river deposits. The intimate relationship between the Lorraine and the highest bed (Oswego sandstone) of this formation, indicates that the age of this formation is Lorraine. The Bald Eagle conglomerate is everywhere succeeded by the red shales and sandstones of the Juniata formation. In southern Pennsylvania this overlaps the preceding formation and rests directly upon the Eden sandstone. The forma- mS cvence, Ne 9:5) ViOln XOMEXS) pHsi55- re PHYSICAL AND FAUNAL EVOLUTION 71 tion here contains remnants of the Lorraine fauna with Byssomichia radiata and other types. These beds are clearly the lower Juniata, for the base of the series is seen in contact with the Bald Eagle con- glomerate not far away. The maximum thickness of the Juniata in central Pennsylvania is from 1,000 to 1,200 feet. On the Niagara, the corresponding Queenston shale is 1,100 feet thick, and it thins away almost wholly before reaching Michigan, where only a few red beds mark the summit of the Ordovicic. The Juniata has all the characters of deposits in arid regions. The total absence of fossils, except where, at the beginning, a lagoon extended north into Pennsylvania, is a striking feature. That fossils could be preserved in the formation is proved by the occurrence Appalachian Region Se a a Interior Region == =dIuniata ——— Marine Series Continental Series Fig. 1o.—Diagram showing relationships of marine and continental upper Ordo- vicic and lower Siluric strata. The conglomerate beneath the Juniata is the Bald Eagle, and beneath it is the Eden sandstone. of Lorraine species in the basal beds. Their absence from the others must then be taken as indicating that none were inclosed in the strata. This absence of fossils, together with the character of the beds, their red color, frequent mudcracks, and numerous clay slugs or “Thongallen” in the sands, and the aeolian cross-bedding, all point to a continental origin, under conditions of semiaridity and tropical climate. That the Juniata and Queenston beds are equiva- lent, and were formed under the same physical conditions, cannot be doubted. Their correspondence in thickness indicates an almost complete equivalency. They may, however, have distinct sources, one in the southeast and the other in the north. In western New York the Queenston shales are succeeded by the true Medina sand- stones and green shales, which are partly fossiliferous, carrying a true 72 AMADEUS W. GRABAU Niagaran fauna. ‘This fixes the age of the Queenston and Juniata as Richmond, so far as their major portion is concerned; though, as already noted, the lower part must be considered as Lorraine (see Fig. 10). In eastern Tennessee a second deposit of red sands of this period forms the Bays sandstone. This is from 1,100 to 1,300 feet thick in its maximum development near Loudon, but thins away by over- lap in all directions. In some localities, as at Walker Mountain, it is fossiliferous, carrving the late Lorraine fauna with Byssonychia radiata, Modiolopsis modiolaris, etc. Wherever the contact with the underlying Sevier shale is exposed, it is seen to be a gradational one, the fossils extending part way up into the red beds. The basal white bed, comparable to the Bald Eagle conglomerate, if it ever existed here, was overlapped by the Bays, the portion east of the overlapping edge having been removed by erosion. The Bays may be regarded as an independent fan, or group of fans, of red sedimentation with a distinct center of supply. The correlation of this series of continental sediments with the contraction of the sea known to have occurred in Upper Ordovicic time has not yet been attempted. It is not improbable that the initial uplift of the land which caused the retreat of the sea, also initiated the strong river-activities which resulted in the formation of the Bald Eagle conglomerate and sandstone. This probably corresponded to the period of folding of the Ordovicic and earlier strata in New England and northward. If that is the case, the emer- gence was probably post-Trenton, falling in early Lorraine (Frankfort or Eden) time and extending toward the end of Lorraine time. The period of red sedimentation in the east may have coincided with the period of erosion in the upper Mississippi and Rocky Mountain areas, and deposition of the Richmond in the narrow interior basins. The late Richmond expansion may coincide with the climatic change indicated by renewed river deposits of white quartzose material. D. THE LOWER SILURIC OR NIAGARAN The following divisions of the New York Niagaran are in common use as the North American standard: Guelph, Lockport, Rochester, Clinton. PHYSICAL AND FAUNAL EVOLUTION 73 The Clinton of the best known section, that of western New York, begins with the true or Upper Medina, which, along the Niagara River, admits of a number of subdivisions, which are, however, of only local significance.t The total thickness is nearly 125 feet, with 25 feet of white quartzose sandstone (Whirlpool sandstone) at the base, and about 8 feet of a similar sandstone at the top. The middle series consists of red sandstones and green and gray sandstones and shales. The red sandstones generally show aeolian cross- bedding and appear to have accumulated above water. The green sandstones and shales are fossiliferous. The white Whirlpool sandstone exhibits beach features,? and probably marks the advance of the sea, though it is likely that the sand was originally dune sand, as suggested by A. W. G. Wilson. The fossils are generally most abundant in the shales and thin- bedded sandstones. The heavy-bedded sands are either free from fossils or have only scattered shells of Lingulae. At Lockport and elsewhere some layers are crowded with gastropod shells. The characteristic fossil, Arthrophycus harlani is everywhere in New York restricted to the upper beds just below the upper white sandstone. The fossils so far obtained from the Medina are: Arthrophycus harlani Conr.; A. sp.; Daedalus several species; Scolithes verticalis Hall; Dictyolithes beckii (Conr.); ““Fucoides” aurijormis and “F.” heterophyllus; Holopea fragilis Hall; Lingula cuneta Conr.; Whitfield- ella oblata; Camarotoechiasp.; Uncinulus stricklandi (Sowerby) ; Plec- torthis medinaensis sp. nov.; Rhipidomella sp.; Pentamerus sp.; Modiolopsis orthonota; M. primigenius; Pterinea cf. emacerata; Pleurotomaria pervetusta Conr.; P. littorea Hall; Holopea (?) conridea; Bucanopsis trilobaius (Conr.); Oncoceras gibbosum; Orthoceras sp.; O. multiseptum Hall; Ascidaspis sp.; Dalmanites sp.; Isochilina cylindrica Hall. This is a Lower Siluric fauna, and favors more especially the Clinton and Rochester faunas. It is so far known only from western New York, with the exception of Arthrophvcus harlani, which is widely distributed. In western New York this species occurs at the top of a heavy-bedded unfossiliferous sandstone with an aeolian type t See Bull. 45, New York State Museum, pp. 88-95. 2H. L. Fairchild, Amer. Geol., Vol. XXVIII, 1909. 74 AMADEUS W. GRABAU of cross-bedding; and just below the upper white quartzite. In east- central New York it is found at the base of the Oneida conglomerate, which is the approximate equivalent of the upper white sandstone of Niagara. In the Appalachians, it is found mostly in the upper part of the Tuscarora and Clinch sandstones, the stratigraphic equivalent of the Medina. Sarle’ has recently interpreted this structure as due to worm borings. So far as I have observed in the field, the raised ridges of this fossil always occur on the under side of the sandstone layers, representing, therefore, the relief molds of grooves generally formed in the clays beneath. These grooves had a median ridge and a regular succession of transverse ridges separated by broad concave grooves. A similar structure, known as Climatichnites trails, but of a much broader type, occurs in the Potsdam sandstone of New York. Woodworth? has suggested that it represents the trail of an animal comparable to some extent to modern Chiton. There are no known remains of organisms in the Medina or Clinton capable of making such an impression, and the organism which made it either had no parts capable of preservation or else it was a terrestrial type frequenting the shores and sandy wastes, where it left its trail in the mud, but not its remains, just as the Triassic Dinosaurs left their footprints but seldom their skeletons. The Tuscarora has a thickness of 820 feet in Logan’s Gap, Jack’s Mountain, Mifflin County, Pennsylvania, but thins perceptibly west- ward and southward, being 400 to 500 feet thick in Bald Eagle Mountain and 287 feet in Wells Mountain and the Pennsylvania- Maryland line. This thinning appears to be due to failure of the lower beds, showing a true case of non-marine progressive overlap. In New York, the upper part is represented by the true Medina, which has a thickness of 125 feet, and begins and ends with a pure white quartz sandstone. More strictly speaking, the upper white sandstone alone represents the true Tuscarora, but the lower beds, still partly red, and the shales, probably are the equivalent of the lower reddish sandstones and greenish shales underlying the true white Tuscarora, and sometimes referred to the Upper Juniata. The Oneida conglomerate of central New York, 40 feet thick, is likewise t Rochester Acad. of Sci. Proc., 1906, No. 4, p. 203. 2 New York State Pal. Rep., 1907, Bull. New York State Museum, No. 69, p. 959- a i j j N q q i ; PHYSICAL AND FAUNAL EVOLUTION 75 the representative of the upper part of Tuscarora, though it may have had a more local origin. All of these beds, including the basal white Bald Eagle formation, belong to the much-washed and reworked type of continental sedi- ments, in which concentration of the indestructible quartz had been brought about by long exposure, resulting in the decomposition of all the other minerals, and the removal of the resultant clay and dust by wind and running water. The Clinton shales succeed the Oneida conglomerate in Oneida and Herkimer counties, New York, and the Upper Medina quartzite in western New York. In the southern Appalachians, the series is largely composed of sandstones (Rockwood), highly impregnated with iron, and often containing beds of workable iron. It is generally succeeded by late Siluric (Monroan) or by Helderbergian or later beds, there being a pronounced disconformity at the summit of the Rockwood throughout. That part of the series in Virginia is of continental origin is indicated by the general character of the rocks, but marine intercalations are not uncommon. In some cases in eastern Tennessee the iron ore itself is fossiliferous, having replaced a marine limestone. In such cases the bulk of the formation is shale. In no case is the original thickness preserved since the formation is everywhere bounded above by an erosion plane. In northern Virginia today the thickness is 750 feet (Piedmont folio), and not over 4oo feet in southern Virginia. In southern Tennessee and northern Georgia it is from 1,100 to 1,600 feet thick, decreasing westward and north- ward. With our present knowledge of the formations, it is safe to say that the eastern sandy phase represents near-shore deposits, if not actually continental conditions, formed probably at the em- bouchures of several Appalachian rivers; and that westward these deltas merged gradually into true marine deposits, mainly sands and clays, with some limestones intercalated. ‘That the Rockwood repre- sents more than the Clinton of New York cannot be questioned. Where the series is developed in its totality, it probably represents the entire Niagaran, if not a part of the Salinan as well. Along the Alleghany front, fossiliferous shales and iron ores represent this series, with a thickness of not less than 1,000 feet, on the western branch of the Susquehanna. The lower series, 700 feet thick, consists mainly of 76 AMADEUS W. GRABAU fissile shales, including an iron sandstone, and with Buthotrephis in the upper part. This is succeeded by 110 feet of calcareous fossilifer- ous shales; and this by 230 feet of fossiliferous shales and limestones with a Niagaran fauna. Above this follows 350 feet of red shales, probably representing the Upper Salina, and separated by a hiatus from the fossiliferous Niagaran shales. In eastern New York, at Swift’s Creek, the type locality for the Clinton, this formation is 226 feet thick and is followed by 5 feet of Niagaran and then by the red shales of the Upper Salina. On the Niagara River the Clinton shale with the two succeeding limestones has a total thickness of 32 feet, followed by 68 feet of Rochester shale. The total of the Niagaran, including the Guelph, is from 270 to 325 feet, as shown by borings. This is followed by Lower Salinan. In the Rochester region the Clinton has a thickness of 80 feet, includ- ing the Irondiquoit or upper limestone (17 feet), which Chadwick refers to the Rochester. The eastward thinning of the Upper Nia- garan beds indicates either that these beds were eroded before the deposition of the red shales, probably during the Shawangunk epoch (see beyond); or that the Rochester-Lockport of the West is in part represented by Upper Clinton in the East. The Guelph element may never have extended to the Clinton type region, which may have been above water and so subject to erosion. The most typical section of the North American Lower Siluric or Niagaran is found in Wisconsin, where the series exceeds 700 feet in thickness and is wholly calcareous. At the base of the series, however, in a few localities, as at Iron Ridge, occurs a remarkable iron ore, composed of flat lentils of varying size and heaped together in a mass strongly suggestive of dune history. This idea is borne out by the position of these pellets, which are not laid flat, as would be the case if they were deposited by water, but are placed in all positions. Cross-bedding and irregular wedging-out of Jayers and a rapid thin- ning away of the entire mass, further suggest an eolian origin. There are no fossils in the ore, and it rests upon an uneven surface of the Upper Ordovicic, with a layer of highly polished clay pebbles marking its base. The interpretation of this formation that I am at present able to advance is that of dunes of calcareous pellets of concretion- ary or phytogenetic origin, similar to the odlite dunes of Great Salt PHYSICAL AND FAUNAL EVOLUTION ag Lake and other regions; and that these dunes were subsequently altered, by replacement, to iron ore. The series of limestones overlying this basal bed, or resting directly upon the Ordovicic, is for the most part richly fossiliferous. Some of the beds, as the Racine and the Coral Beds, are characterized by reefs of Stromatoporoids and other corals, widely distributed and connected by more or less barren lime sands (calcarenytes) which resulted from the erosion of the reefs. Some beds are of shallow- water origin and bear the marks of periods of exposure, resulting in the formation of mud cracks, etc. The fauna is more or less uni- form throughout, and the series represents continuous deposition, recording only minor oscillatory movements. Southward we find these beds extending through northern Illinois, Indiana, and Ohio, with a more or less uniform fauna, while further south, in the Cin- cinnati and western Tennessee regions, part of the limestones is replaced by shales and new faunal elements appear. The typical Niagaran jauna.—This is to be found in the strata of the Wisconsin section and in their continuations in northern Illinois, Indiana, Michigan, and Ohio. It is an exceedingly rich fauna, and, as Weller has ably demonstrated, has many elements in common with the Mid-European Siluric. The Stromatoporoids abounded on the reefs of the Coral Beds and the Racine. They have not been much differentiated in Wisconsin, but from other sections, especially Canada and Ohio, a considerable number of genera and species have been recognized. Corals abound, especially Halysites and Favosites, while Bryozoa are most common in the shales of New York and the southern area, Fistulypora making extensive reefs in western New York. The brachiopods, except the large Pentamerus, are likewise more characteristic of the shales. Crinoids, Cystoids, and Trilobites appear to be most common in the lime- stones of the interior. The Guelph jauna.—This fauna demands a special notice, because it is so distinct in its eastern manifestations. The peculiar aspect of the fauna is produced by the great Trimerelloid brachiopods (Trimerella grandis, T. ohioensis, Monomorella prisca, etc.); the peculiar corals Pycnostylus; the large pelecypod Megalomus canaden- sis; the gastropods Pycnomphalus solarioides; and the genera 78 AMADEUS W. GRABAU Euomphalopterus, Hormotoma, and Coelidium, together with various species of Eotomaria and other Pleurotomarioids, and the remarkable Trematonotus alpheus. ‘This represents a new invasion of the interior sea, probably from the rich fauna of northern Europe. In North America the physical conditions accompanying this spread of the fauna appear to have been shoaling of the water and inclosure and restriction of the interior sea. The fauna appears as early as the lower Coral Bed in Wisconsin, while the Guelph element of the Racine fauna is very marked. Tvrimerella grandis, Megalomus canadensis, Pycnomphalus solarioides, Coelidium macros pira, and S phaeradoceras des plainense are among the species which occur in association with the rich Racine fauna. Many of the typical corals, brachiopods, and other types continue into the Guelph in Wisconsin, the fauna not differing markedly from the Racine. In New York Clarke and Ruedemann have found the Guelph fauna intercalated between the normal manifestations of the Niagaran coral fauna (Lockport), and it appears that in the Canadian type region alone does it occur in its purity. THE ATLANTIC AND SOUTHERN NIAGARAN The Atlantic Niagaran has generally been recognized as belong- ing to a distinct province separated by a land barrier from the interior sea. This is made evident not only by the distinctness of the faunas, as exhibited in the Anticosti group and the development in Maine and New Brunswick, but also by the fact that the entire interior Appalachian region contains only shallow-water or continental deposits, indicating a continuous land mass in the East. That the Anticosti fauna nevertheless communicated with the interior is shown by its occurrence in Georgia and elsewhere in southeastern United States. This occurrence represents either a distinct embayment from the Atlantic, or the fauna migrated into the interior, going around the southern end of Appalachia, which may then have been separated from South America. An invasion of the interior from the south is indicated by the fauna of the Cape Girardeau or Alexandrian’ forma- tion of Illinois and Missouri, and perhaps also by the fauna of the 1 See T. E. Savage, Amer. Jour. Sci., Vol. XXV (1908), pp. 431-44; Schuchert, Jour. Geol., Vol. XIV (1906), pp. 728, 729. PHYSICAL AND FAUNAL EVOLUTION 79 St. Clairt limestone of Arkansas. The Alexandrian series of Savage contains many types unknown from the true Niagaran, some Ordovicic genera also being present (Rafinesquina, Platystrophia, Rhynchotreta, Zygospira). Few typical Niagaran species occur, but the presence of the genera Favosites, Atrypa, Whitfieldella, Homoeospira, Schuchertella, Chlorinda, and Lichas (Metopolichas) indicates the Siluric age of this fauna. It probably represents an invasion from the south before the Niagaran transgression from the north had reached the southern Illinois region. Northward, in central and northern Illinois, this fauna seems to be wanting, the true Niagaran fauna here succeeding the Cincinnatian. The Alexandrian is succeeded disconformably by 30 to 75 feet of limestones with a Lower Niagaran fauna. A transgression is indicated by the fact that ‘where the formation is thinnest, it is the lower, and not the upper layers that are absent.”? The Niagaran fauna includes: Favosites javosus, Halysites catenulatus, Atrypa rugosa, Orthis flabellites, O. cf. davidsoni, Plectambonites transversalis, Stricklandinia triplesiana, and Triplesia ortoni; which grouping, as stated by Savage, corresponds to that of the Clinton of the Dayton, Ohio, region. The invasion of the interior by a southern fauna, in later Niagaran time, seems to be indicated by the later Siluric formations of Tennessee and possibly in part by the Louisville limestone of Indiana and Kentucky. The higher beds of western Tennessee, called by Foerste3 the Brownsport beds, and subdivided into the Beech River, Bob, and Lobelville formations by Pate and Bassler* contain faunas apparently not found in the typical or northern Niagaran formations, and which are well developed in the underlying series, named, in ascending order, Clinton, Oswego, Laurel, Waldron, Lego, and Dixon. t Gilbert Van Ingen, ‘‘The Siluric Fauna near Batesville, Ark., Part I,” School of Mines Quarterly, Vol. XXII (April, t90r), pp. 318-29. 2 Savage, op. cit., p. 435. 3A. F. Foerste, ‘‘Silurian and Devonian Limestones of Western Tennessee,” Jour. Geol., Vol. XI, pp. 554-715. 4W.F. Pate and R.S. Bassler, ‘‘The Late Niagaran Strata of West Tennessee,”’ Proc. U. S. Nat. Mus., Vol. XXXIV, pp. 407-32. See also Roemer, Die silurische Fauna des westlichen Tennessee, in which the fauna of these higher beds is described. 80 AMADEUS W. GRABAU E. THE MIDDLE SILURIC OR SALINAN This is typically known only from New York, Michigan, western Ontario, northern Illinois, and Ohio, and is everywhere a series of more or less calcareous shales and gypsiferous beds, with salt beds up to too feet in thickness. The maximum development is in central New York and southern Michigan, where it exceeds 1,000 feet in thickness. In western New York it is only 350 feet thick. The only fossils known from the beds are from the lower (Pitsford) shales, where they represent the last survivors of the Guelph. They are chiefly Eurypterids (Hughmilleria, Eurypterus, etc.) and occur in muds alternating with dolomites carrying a Niagaran fauna. The Eurypterid fauna also occurs in the mud layers in the Shaw- angunk conglomerate, which hardly admits of any other interpreta- tion than deposition by torrential rivers. This would make the Eurypterid fauna a fresh-water fauna, an interpretation which best corresponds with the distribution of these fossils geologically as well as geographically. The Salina series is best understood as a desert deposit. The absence of organic remains (with the exceptions noted), known to be abundant in all modern salt deposits of sea-margin origin; the thickness of the salt beds; their limitation to circum- scribed basins,‘ the red color of the lower shales, their mud cracks, “Thongallen,” etc., all point to a continental origin. The absence of true marine strata of Salina age? and erosion of the surrounding Niagaran beds further indicate that North America was above water. The salt was derived from the marine limestones of Niagaran and earlier age. THE GREEN POND SHAWANGUNK CONGLOMERATES AND SUCCEEDING RED SHALES The general retreat of the sea at the end of Niagaran time was marked in the east by an uplift followed by continental sedimen- tation. The series began with a conglomerate (Green Pond) 1,500 feet thick in northern New Jersey, but thinning northward to 500 feet at Ellenville (Shawangunk conglomerate), to 200 feet at Rosen- dale, and to nothing at Rondout. Southward and westward it thins t See Walther, Gesetz der Wiistenbildung. Lack of space forbids the full discussion of this interesting problem. It will be treated at length in another paper. 2 The so-called marine Salina of Maryland is of Monroan age. ee ee i PHYSICAL AND FAUNAL EVOLUTION 81 to 700 feet at the Delaware water gap, to 4o0o feet at the Lehigh, and to less southward. The thinning is by failure of the lower beds, showing this to be a true non-marine overlap, and therefore stamping the series as of river origin. The Eurypterid layers in the upper beds are probably contemporaneous with the basal Eurypterid beds of the Salina of New York. The succeeding series of Longwood shales resembles the Juniata-Queenston, and, like it, has all the ear- marks of a continental series formed under semiarid conditions. They thin from 2,385 feet in New Jersey to 120 feet at Cornwall, 75 feet at High Falls (High Falls shale); and 25 feet at Rosendale, and disappear farther north. Southward they thin likewise, while westward only the upper 400 feet of the series is shown in the red Lower Salina shales of Ithaca and Syracuse, New York, where they are succeeded by salt deposition, and less than 200 feet at Buffalo. Like the conglomerate, the shales thin by failure of the lower beds, i. e., by non-marine overlap away from the source of supply. F. THE UPPER SILURIC OR MONROAN This is typically developed in southern Michigan, Ohio, and west- ern Ontario, where it is divisible into Lower Monroe or Bass Islands series, 500 feet thick, or more; middle Monroan or Sylvania sandstone 30 to 150 feet thick; and Upper Monroan or Detroit River series, 300 to 400 feet thick.’ The entire series is involved in gentle folding of early Devonic age, the Dundee resting upon the eroded surfaces of various members of the series. The Lower Monroan represents an invasion from the Atlantic across Maryland, Pennsylvania, and southern Ohio, to Michigan and probably Wisconsin. Western Ontario was involved, but apparently not western New York. ‘The fauna is Upper Siluric, genetically related to the Manlius limestone fauna, and, like it, representing an Atlantic type. The Upper Monroan fauna, on the other hand, is of a distinct type, especially in the lower members (Flat Rock, Amherst- burg, and Anderdon beds). Besides being related to the later Nia- garan fauna, it has a new coral and brachiopod element suggestive tSee Sherzer and Grabau, Bull. Geol. Soc. Amer., Vol. XIX. The full dis- cussion of these formations and their fauna will appear in the report of the Michigan Survey. 82 AMADEUS W. GRABAU of Devonic affinities. This is further shown by the occurrence of Panenka and Hercynella in these beds. The highest division (Lucas) is characterized by gastropods, most nearly related to late Siluric types of northern Europe. The Amherstburg beds of the Upper Monroan appear to be the chronologic equivalent of the Cobleskill of eastern New York, several characteristic species being common to both. It represents the junction of an eastern and a western sea, and a commingling of the faunas of both. The typical Upper Monroan coral and brachiopod fauna seems to have invaded Michigan from the northwest, a somewhat similar fauna appearing near the headwaters of the Saskatchewan. In Pennsylvania the Lewistown limestone appears to represent this horizon. The Sylvania sandstone has all the characteristics of a wind- drifted sand. Its cross-bedding is of the aeolian type, its grains well rounded, pitted, grooved, and of uniform size; there is a total absence of impurities, and all the characteristics compare favorably with those of the sands of the Lybian desert of today. It indicates a period of land condition between the retreat of the Atlantic embayment (Lower Monroan) and the Pacific invasion of Upper Monroan time. G. THE LOWER DEVONIC The Lower Devonic comprises the Helderbergian and the Oris- kanian of Clarke and Schuchert. The Helderbergian includes the Coeymans, New Scotland, Becraft, and Port Ewen. The latter is transitional to the Oriskany, and Chadwick proposes to unite it with that formation.t ‘The Coeymans is the direct depositional successor of the Manlius, there being frequently a transitional zone between them, with a commingling of the fossils. The former extent of the Coeymans can be estimated from its occurrence at Syracuse and the uniform character which it maintains in that region. ‘This indicates that the western shore of the Helderberg sea was west of Syracuse and perhaps in the region of Buffalo. The eastern and northern limit of the formation is indicated by its mergence into shore deposits in New Jersey, and the southward overlap of the later formations, t Science, N. S,, Vol. XXVIII, p. 347. PHYSICAL AND FAUNAL EVOLUTION 83 the Virginia, western Tennessee, and Oklahoma occurrence of this series beginning with beds carrying a New Scotland fauna. The emergence of the North American continent at the end of Siluric time was accompanied by the first pronounced doming of the Cincinnati region and basining of the Michigan area. Local oscil- lations seem to have preceded this, but the first great movement apparently did not occur until the end of the Siluric. Between the Michigan basin and the Cincinnati dome were formed the Wabash anticline and the minor folds of Michigan, Ohio, and Canada. When these regions were again wholly submerged in Mid-Devonic time, the deposits of this later epoch came to rest on the beveled surfaces of various Siluric members (see Fig. 11). A subsequent movement Northern Michigan Southern Michigan ) Northern Ohio 1 Central Ohio Southern Ohio oS) hale == SS ooo 2 i SSS Put y nyt rae SS Tee and Ty 5 = Greenfie1d-3 Fig. 11.—Section from northern Michigan to southern Ohio, showing the rela- tionship of the Middle Devonic to the Siluric and of the Upper to the Middle Devonic. O = Olantangy shale. in the same direction, at the end of Paleozoic time, threw the later beds into similar folds, while emphasizing those of the earlier series. A marked hiatus occurs between the Helderbergian and Oris- kanian. ‘The former series is beveled, so that the Oriskany comes to rest, as it extends westward, upon lower and lower members of the Helderbergian, and finally upon the Manlius, and still farther west upon the Akron dolomite (Cobleskill). This beveling is in part due to retreatal ‘‘off-lap’’ but also to extensive erosion which indicates a time-period of some magnitude for the Oriskany. The deposi- tional equivalent of this hiatus is found in the Gaspe region of Canada, where 550 feet of Oriskanian (Grand Greve limestone) follows tSee Grabau, Bull. 92, New York State Museum. 84 AMADEUS W. GRABAU 1,200 feet of Helderbergian (St. Albans and Bon Ami limestones), the succession being a conformable one.' The Oriskany of the United States is mostly a sandstone, often of pure quartz grains, at other times calcareous. The source of the sandstone is to be sought in the sandstones of the eastern extension of the Siluric and Ordovicic formations, and perhaps in the exposures of the St. Peters and the Sylvania. It seems most likely that the distri- bution of the sand over eastern North America was largely effected by wind, during the long period of erosion preceding the submergence of the continent. On the westward extension of the Oriskany sea these accumulated sands were reworked and were transformed into the fossiliferous marine sands which they are found to be today. In the east, after a short period of sedimentation, an extensive accumu- lation of black muds occurred, forming the Esopus-Schoharie shale series. This has its greatest thickness at Port Jervis, whence it thins away in all directions, apparently by overlap. Since the source of the material was clearly in the east, and the overlap is toward the west, north, and south, the formation must be a subaerial fan. This is further indicated by the general absence of fossils, except for occasional intercalations, such as would be expected in a fan of this kind, probably rising but slightly above the level of the shallow Oris- kany sea. The continuance of the Oriskany invasion is found in the spread of the limestone with the Schoharie fauna and the succeed- ing Onondaga submergence. During Onondaga and Hamilton time, continuous deposition and spreading of the seas went on, but at the close of the Middle Devonic, renewed emergence affected most of southern and southeastern United States, accompanied by erosion. This again was followed by the slow resubmergence, which commenced from the north and slowly advanced southward and eastward. The basal member of this transgressing series is the black shale, which, in northern Michigan, is of Lower Devonic (Genesee?) age, but becomes of later and later age southward, at the same time resting always on lower strata. Thus late Upper Devonic (Portage) black shale rests on Lower Hamilton in southern Michigan and northern Ohio; still later beds (Chemung) on the Onondaga (Columbus) «See J. M. Clarke, ‘“‘Early Devonic History of New York and Eastern North America,” New York State Museum Memoir 9, 1908. PHYSICAL AND FAUNAL EVOLUTION 85 in central Ohio; while the highest beds rest on Monroan or even Niagaran, in southern Ohio. Continuing southeastward, the black shale rises in the series, until in eastern Tennessee it is of Lower Mississippic age, and rests on Lower Siluric or on Ordovicic strata.' (Fig. 11). DISCUSSION PROFESSOR CALVIN I have studied the St. Peter sandstone in Iowa, Wisconsin, Minnesota, and Illinois, and nowhere have I seen any marked indications of cross-bedding such as would be consistent with an aeolian origin of the formation. In Iowa and Minnesota there are few structural bedding planes seen in fresh sections, but those that do exist are always horizontal and parallel. Bedding planes are more numer- ous in this sandstone west of Ottawa, IIl., but they are all precisely of the character one sees everywhere in aqueous sediments. When the St. Peter is exposed on sloping hillsides, by a process akin to exfoliation, it breaks off in thick flakes parallel to the exposed surface and so often presents a false appearance of cross- bedding; but this feature has no relation to the original structure. One hardly needs to go to the Libyan desert to ascertain the characteristics of aeolian sands. The region around the south end of Lake Michigan affords ample opportunity, nearer home, to study the structural features and topographic forms of wind- blown deposits. I have seen nothing in the St. Peter suggesting similar origin. Furthermore, the St. Peter occasionally contains marine fossils, as shown by Winchell and Sardeson. REJOINDER PROFESSOR GRABAU Most writers on the St. Peter have described it as showing marked cross- bedding. It is not always readily recognized and is often overlooked in sand- stones of this type. But even if there were no cross-bedding in the known exposures, this would be no argument against the eolian origin of the formation, since modern eolian deposits often lack such a structure—and, indeed, sometimes lack all bedding. The comparison with the sands of the Libyan desert is made because they represent precisely what is believed to be the origin of the St. Peter and Sylvania. These sands are derived from an older sandstone—not from glacial sands as are those of Lake Michigan. They show a similar purity, rounding, and uniform size as found in the St. Peter and Sylvania. Finally they have been transported a great distance and rest with a sharp contact on eroded limestones, often including the weathered-out fossils of this limestone in their base. The fossils obtained from the St. Peter were, as noted in the text, obtained from the lower and upper parts, the latter of the Stones River type, included in the rewashed upper sands on the advance of the Stones River sea over the old dune area. The fossils included in the basal part are either weathered-out Beekmantown or included in the sands during the retreatal phase. Such inclusions are to be expected in deposits of this type. «See Grabau, “‘Types of Sedimentary Overlap,” Bull. Geol. Soc. Amer., Vol. XVII, pp. 593-613. GRABAU AMADEUS W. 86 squires soddq uvISIUSEIT 1OMOT Ja}jag ‘JS 10MO'T JaArYy sauojs roddq hits iL (3 Bus[ex)~juLsRI[g JUIOg PQ “jUoIsIq] ¢ wepa pue SRE, altiasteyy BJaYONDEJA|-PuOWY ITY TT ‘A2qTeA iddisstsstpy uodey reddy neuubuld JOLIO}UT (payseul| uajo) AjtuLI10J|UOIsI, pue sniyery 49}9qg "IS teddy suquieg ssddq n @ uMO} 3 -uvMysog 3 © r<) a Ayuroyuoouy) pur snyerpy| Ajtw0JUOoUY) pur snjzerpy UMOJULWTYIG IaMO'T dip jo aduepsoosip yNoyIM ‘AIWIOJMODUN [eUOIsOIa UL SI ‘Neqviry Aq pouyap sv ,,‘AjWIOJUOISIp,, W at re) WIQUMie)-a1g dquieg-aq suquiey siaddyQ -qng Qa oO i=) + aMUojod ,, Weps}og,,, STP PBSIIOY T, aT UMOJUCLU YI | (2) (©) fee) ce ULIUMOJUTWYIIG 10 19M0'J 3 Ss Ss Bs A}WULOJUOISICT O Qs qs pue snjyery B® 5 & PAG S os Ss |) We) B go 5 6. y Blo On a oe Sa Seo eI < Kze ° Sas YO 5 a lee = os vIpwMeg 9 s = =) MOT attamoy | i i] S| OO AMY TH = JOATY PUA LATY YUL 5 it Ealetee ss ae RS eS (@ uojual UO}UILT, uojual J, 20 enn aie WosyUeI joyyursy = IIIS i IUILIIO'T JUILIIO’T et i Te W PIPE) ss ,OBIMSO ,, [BSE O3IMSC) [seg 54 a eyetunf a[eysS uojysuaang) purée tuo], ‘ude d uJaqjNOS A ueiyoejeddy YIOR MAN Us9}s9\\ DUS AE aoe Aaye,, urejduieys I ATAVL NOILVTAYAOD 87 PHYSICAL AND FAUNAL EVOLUTION sajeysS uospny saeyg Wopyuery sajeys uoySusan?) . puowMysIy Aywii0jyuoou pq, uv Ajjesouad pur snjeipy RR AER GS) AyituroyuoosIqg pue snzPIET (qo11]s-suas) dUOJspuUrS BUIPIT] AjUIIOJUOISICT PUR SNILIFT PILBVIN ayeINWO[SUO.) BpIUC, Su0ISaUUr'y “uoyuO | aptadkeyy | = uojul[D 2 : Jajsayo0y | vysoyne sy, (uonsas-adA} Jo) uojquttD DUP sePHS MOUND yodys07T aulory vICSPIN ydjang | ydjeny | 5° AyuIoyuodsIq—snjelpy (qunsuvaeys) ILIMNUO[SUOD puog uwas1H (S9qeYS STA 431) SajvyS poomsuo’y Alu soyuoosiqy ‘snqyeiyy PrOS uouldA asngvihs snqiwed wulles Aj usojuoosiqa—snyelpy a[epussoy “ISO MEISPIGOD UMO}SIMIT jnopuoyY sulyuryy AWIOJUOISIGE—snyqwipy AWIOJUODSI(T puv sNyeIyy JUOJSPURS JoIVMOUULE, aeys surwArig SOS EMANTL [MP ERMT(C) DUTIJ1IIVA\ JNOpuoY, QUOJSOWIT snipuryy DUMIPIo}e AA 91719q aywojoq] uoLYy Aywusz0juoosiqg pue snjqeiyy ‘uuag pur ssrdquopay sayqny pure _winsdfxy \yes—eurpes- Aqws0uoIsI—SNqeIE] aWO[Od ppeyus1y ayeys soyyoours 7, satag Avg-ul-jng SOLIIG JOA UISTR YY S119 PUelsL sseg AYLWIOJUOISICT puv snyzerpT QUOJspURS BIUBATAS AjIUILOJUODSIC, puUR SNyeIPY dMUO[OG YoY WL SdLI9G aUO}soW'T UopIapuy JOARy OUT Sind |s1syuy HOH at ayWIOjoq, svon’T AjtUIOJUODSIC, puw SNyeIpT YIOA MIN [eUGQ—Iseq YOK MIN [eUID pur ysa\y epeury pur ‘oryo “uesiyoI] ——— II ATAVL NOILVIAAAOO uvieseIN 10 1aMOT ueUulyes 10 a[pPr Olas uvoiuopy 10 raddq | JIOIA -OdxO PALEOGEOGRAPHIC MAPS! MIDDLE ORDOVICIAN AND SILURIAN RAILEY WILLIS U. S. Geological Survey 3 AND 4. MIDDLE ORDOVICIAN* AND SILURIAN? The passage from the upper Cambrian to the Ordovician appears to be marked in many localities by inconspicuous but notable evi- dences of non-deposition or erosion which may be attributed to submarine scour or the actual subaérial denudation of low-lying lands. The phenomena differ from those which commonly accom- pany marked continental deformation. They are believed to have resulted from the deepening of ocean basins which gave rise to a widespread ebb of the epicontinental seas. Effects of continental warping of a subordinate character may naturally have accompanied the sub-oceanic movements. ‘The conditions of oceanic circulation which result from a consideration of the probable distribution of seas and lands are those of general northward currents flowing from the Gulf of Mexico through to the Arctic. They carried with them the characteristic middle Ordovician fauna, which, however, developed local diversities in the eddies of the North American archipelago. In contrast to the central marine currents and their fauna we have the polar southward-trending return currents which may have been congenial to the graptolites. Their distribution would seem to ex- plain the similarity of graptolite faunas in the eastern and western troughs. A peculiar circumstance is suggested in the occurrence of the graptolites in Arkansas. This is recognized on the map by the crossing of the arrows indicating marine currents. It is a well- established fact of oceanography that marine currents pass over or under one another, and this fact affords a possible explanation of the relations which appear to have existed in Tennessee and Arkansas. As a supplemental hypothesis the student should consider Professor « Based largely on data furnished by C. D. Walcott. 2 Based on data furnished by Dr. E. M. Kindle. 88 PALEOGEOGRAPHIC MAPS GZ ‘4, RRR FRR RQ ; ISS —— RS v SN SN WSS: ; LEGEND | OCEANIC BASINS | MARINE WATERS (EPICONTINENTAL) SEA OR LAND, MORE LIKELY SEA | LAND OR SEA, MORE LIKELY LAND } LANDS INDETERMINATE AREAS POLAR MARINE CURRENTS EQUATORIAL 120) y SS SY ASS S NN NN CREM WN: ti LI Ue go BAILEY WILLIS ee AWN SAE NS So SEAN SAS SN W ‘ \\ SSSA SY) W\ b> SX S\N NW NORTH AMERICA _ a oniles LEGEND OCEANIC BASINS MARINE WATERS (EPICONTINENTAL) SEA OR LAND, MORE LIKELY SEA | LAND OR SEA, MORE LIKELY LAND "{ LANDS INDETERMINATE AREAS POLAR See EQUATORIAL ———_>> Toe 10g? MARINE CURRENTS 100 IG 1% x xo ERK PORK KD etatatatenes teste, YS NSS « \ 7-—— NORTH AMERICA LEGEND OCEANIC BASINS MARINE WATERS (EPICONTINENTAL) SEA OR LAND, MORE LIKELY SEA LAND OR SEA, MORE LIKELY LAND NE : OXY NE b Ses io LANDS Z > : TEMPORARY LAND TT) “ INDETERMINATE AREAS 5 HA , POLAR ——._ CONTINENTAL DEPOSITS, SOMETIMES RORINE (CURRENTS EQUATORIAL = —————_ INCLUDING MARINE SEDIMENTS 120° 110) 100 90° BAILEY WILLIS 198 ES SOMETIM INCLUDING MARINE SEDIMENTS p LY, n = n a 2) Oo Q a 4 f < i & a Yip z A G [I Lilo Zz W fo} oC S Li rar S POLAR EQUATORIAL, END MORE LIKELY SEA ENTS LEG INS ERS (EPICONTINENTAL) s SEA. MORE LIKELY LAN NORTH AMERICA BA sAND LANDS UPPER CRETACEOUS MARINE CURR I ——— OCEANIC MARINE WAT SEA OR LAND OR INDETERMINATE AREAS PALEOGEOGRAPHIC MAPS 199 has been suggested except that a land mass diverted the ocean current. The position of the supposed land was southwest of Mexico and is indicated by the dotted area. North America was submerged over extensive areas during the Upper Cretaceous. From Cape Cod to Texas the Atlantic and Gulf coasts of the preceding period were transgressed by the sea. From the Gulf to the Arctic marine waters spread over what is now the site of the Great Plains and in the United States that of the Rocky Moun- tains. The Pacific extended its limits in California and Oregon; farther north, however, from British Columbia to Alaska the land gained. In the central West, from New Mexico to Alberta the invasion of the sea was followed by emergence of the area ruled on the map for continental deposits. The surface of the area was built up by sedi- ments which were derived from uplands west of it, and which accu- mulated about as fast as the bottom sank. The area thus formed a coastal plain, extensive marshes prevailed, and the marsh deposits eventually became coal beds. Sea, marshes, and river plains alter- nated in sequence till near the close of the Cretaceous period, when in this Rocky Mountain area certain spots became mountains, the forerunners of the Colorado Front Range, the Black Hills, and Big- horn Mountains of today. East of the Rocky Mountain coastal plain the marine strait pre- vailed to the end of the period. It divided the continent, reduced the northern land area, and admitted warm waters to the Arctic. These conditions favored the mild climate which the northern regions then enjoyed. . The eastern portion of the continent contrasted with the western. Whereas in the west rising lands were eroded, carved into hilly or mountainous landscapes, and yet became more elevated, in the east the surface was a vast plain and remained a lowland. The close of the Cretaceous was marked by a general ebb of the seas that had prevailed over continents, possibly because the ocean basins deepened. In central western North America the land was rising also, and the combined effect was to withdraw the waters of the strait to the Gulf on the south and to the Arctic on the north. CHAPTER ax SUCCESSION AND RANGE OF MESOZOIC AND TERTIARY FLORAS: F. H. KNOWLTON It is of course a truism to say that the transition from the Paleozoic to the Mesozoic is not, as was once supposed, an abrupt or catas- trophic change, but was brought about so gradually that in many parts of the world it is often difficult, if not indeed impossible, to draw any sharp lines. Not only are the rocks lithologically similar, but a certain percentage of life-forms persisted from the one to the other, yet when each system is considered in its entirety there are apparent abundant lithologic and strongly marked biologic differ- ences. It is my purpose to speak briefly of the floras, first of the Mesozoic and later of the Tertiary. Triassic.—Rocks of Triassic age are known in many parts of the world and indicate two types of deposition, a fresh-water, marsh, or lagoon phase, and a marine phase. The former is only, or largely, that which has afforded a flora. The known plants of the Trias are relatively few in number. In North America we have less than 150 species, and the entire Triassic flora probably does not exceed 300 or 400 forms. Owing to considerations, physical and otherwise, concerning which there is not complete agreement, the lower portions of the Trias afford but scanty remains, and it is not until we come to the upper portion, or Rhaetic, that it can really be dignified as a flora. Our North American Triassic flora is believed to belong largely to this portion. ‘Triassic plants have been doubtfully reported from Prince Edward Island, but they are so obviously of Permian types that they may be disregarded. The principal areas are in North Carolina, Virginia, and Pennsylvania, with relatively few in Maryland, New Jersey, Connecticut, and Massachusetts. In the west we have a doubtful plant or two from Wyoming, a considerable number from northern New Mexico, the extensive fossil forests of 1 Published by permission of the Director of the U. S. Geological Survey. 200 MESOZOIC AND TERTIARY FLORAS 201 Arizona, and a very few species from Plumas County, California. Going southward we have small collections from Sonora, from about the City of Mexico, in Honduras, Chile, and western Argentina. In other parts of the world Triassic floras have been found in England, east coast of Greenland, Spitzbergen, North Germany, southern Sweden, Italy, southwestern Spain, Persia, India, China, Tonkin, Japan, New South Wales, New Zealand, and South Africa. What, now, are the characters of the Triassic flora? The domi- nant types of the Paleozoic have largely disappeared. The Lepido- dendrae, Sigillariae, Calamites, Cordaites, Sphenophyllae, and Cycadofilices, so far as ascertained, have all gone, as well as a num- ber of important genera of ferns—Cheilanthites, Mario pteris, Megalo p- teris, etc. ‘The most notable survival from the Paleozoic is the so-called Glosso pteris flora, which has been found with a few associated forms in Rhaetic rocks at Tonkin, the Stormberg series of South Africa, New South Wales, etc. The Triassic flora consists essentially of equisetums, ferns, cycads, and conifers of many genera. A few forms such as Ginkgo, Cla- dophlebis, Thinnfeldia, etc., had a small beginning in the Paleozoic and expanded in the Mesozoic into large groups. But most of the flora is of distinctly Mesozoic and northern origin. It has often been said that the plants of the Triassic are depau- perate and pinched in aspect, indicating unfavorable climatic con- ditions. The paleobotanical facts do not altogether bear this out. In North Carolina, Virginia, and Arizona, there are trunks of trees preserved, some of which are 8 feet in diameter and at least 120 feet long, while hundreds are from 2 to 4 feet in diameter. Many of the ferns are of large size, indicating luxuriant growth, while Equisetum stems 4 to 5 inches in diameter are only approached by a single living South American species. The cycads are not more depau- perate than those of subsequent horizons, nor do they compare unfavorably with the living representatives. The complete, or nearly complete absence of rings in the tree trunks indicate that there were no, or but slight, seasonal changes due to alternations of hot and cold, or wet and dry periods. The accumulations of coal—in the Virginia area aggregating 30 to 4o feet in thickness—indicate long-continued swamp or marsh condi- 202 Ff. A. KNOWLTON tions, while the presence of ferns, some of them tree-ferns, indicate on the whole a moist, warm, probably at least sub-tropical climate. Jurassic.—Coming, now, to the Jurassic, we find in the lower portion indications of a continuation of conditions which obtained in the upper portions of the Trias. The distinctive Paleozoic elements had finally disappeared, and the Mesozoic life-forms were in full swing, expanding in the middle and upper parts of the period into the abundant and widespread flora as we know it. In fact the relative uniformity and wide extension of the Middle and Upper Jurassic flora is one of the most interesting and impressive exhibits that we have. (See map showing approximate distribution of Triassic and Jurassic flora.) There is no paleobotanical evidence indicating the presence of the Jurassic in Eastern North America. In the western interior Jurassic plant-bearing beds occur in the Black Hills, South Dakota, and the Freezeout Hills, Carbon County, Wyoming. We then pass to the Pacific coast, where we have a fine flora near Oroville, Cali- fornia; also northward in Trinity and Tehama counties, California, and Douglas and Curry counties, Oregon. The following is an outline of the world distribution of the flora: Alaska Copper River District Cook Inlet Herendeen Bay Cape Lisburne England Yorkshire France Mamers—northwestern portion Germany Franco-Swabian area Northwestern area Austria-Hungary Steierdorf in Banat Crojie in Galicia Cracow Italy Switzerland Portugal Sweden Bornholm Bjuf Spitzbergen Cape Boheman, 78° —22’ N. Advent Bay, Cape Staratschin Green Harbor King Karls Land 78-707 NE 203 MESOZOIC AND TERTIARY FLORAS dissvin f = sjoq, dISSBILT, = SBURT “SPIOY DISseIN{ puv IISSeIIT, JO uOTINGIysIp syeutxo1dde Surmoys depyY—'t ‘org eal ne 204 F. 2H. KNOWLTON Franz Josef Land 82° N. Greenland Cape Stewart 80° N. Siberia Ust-Balei 51° N. Irkutsk Upper Armour River Lena River District Corea Japan Caucasia Turkestan India Cutch Jabalpur China Tyrkyp-Tag Border Hami Desert Australia New Zealand Louis Philippe Land 63°S. The flora of the Jurassic, while in the main a continuation of that of the late Trias, and consisting of equisetums, ferns, cycads, ginkgos, and conifers, shows the incoming of a number of more modern types in these groups. The cycads were of course abundant and diversified, whence it has been called the age of cycads. The flora is remarkably uniform over wide portions of the world. ‘Thus not far from 50 per cent. of the North American flora—exclusive of the cycad trunks— is the same as that found in Japan, Manchuria, Siberia, Spitzbergen, Scandinavia, or England, and what is even more remarkable, the plants found in Louis Philippe Land, 63° S., are practically the same as those from Yorkshire, England. Some idea of the climatic conditions which prevailed at this time may be gained from the present distribution of certain obvious descendants of the Jurassic flora. Thus Matonidium and Laccop- teris are represented by Matonia of which there are two species living in the Malay region and Borneo; Dictyophyllum, Protorhipis, Haus- mannia, Caulopteris, etc., are closely allied to Dipteris, which has five species living in the eastern tropics; Ginkgo—so abundant in the Jurassic—has but a single living representative in China and Japan. Climatic conditions in Jurassic.—The presence of luxuriant ferns, many of them tree-ferns, equisetums of large size, conifers, the MESOZOIC AND TERTIARY FLORAS 205 descendants of which are now found in southern lands, all point to a moist, warm, probably subtropical climate, though in late Jurassic time the presence of well-defined rings in the tree trunks of species found in northern areas—King Karl’s Land, Spitzbergen, etc.—show that there were beginning to be sharply marked seasons. Wealden._Immediately above what by common consent is regarded as the top of the Jurassic, is a series of fresh-water plant- bearing beds that are of quite wide extent in this country, though different names have been applied in the different areas. Thus the lower Potomac of the eastern United States (including the Patuxent and probably Arundel), the Glen Rose beds of the Trinity division of Texas, the Lakota and Cloverly of Dakota and Wyoming, the Kootenae of Alberta and adjacent Montana and extending into the Bighorn Basin of Wyoming, and the Shasta of California, and Kome of Greenland are practically equivalent in age, and correspond most closely in age with the Wealden of the Old World, which is considered to be a fluviatile or lacustrine condition of the lower Neocomian, the lowest member of the Cretaceous. The flora is a comparatively rich one, aggregating between two hundred to three hundred species, and is composed of ferns and conifers with a fair sprinkling of cycads Equisetaceae, ginkgos, etc. It shows a considerable agreement with the Jurassic, a number of species being common to the two, but on the whole its affinity is rather with the Cretaceous. Cretaceous.—Up to the present point in the geological column the most characteristic and dominant feature of the modern flora—namely the angiosperms—has been absent. In many ways the introduc- tion of this type of vegetation was one of the most important and far- reaching biologic events the world has known. For many years the flora of the Dakota Group and kindred floras was the oldest angiosper- mous flora known in this country, but as there are such a host of appar- ently modern types present, it was presumed that they must have had an ulterior period of development—and such proved to be the case. So far as we now know this flora appears to have had its origin in eastern or northeastern North America, in the Patapsco division of the Poto- mac series. Although the great majority of the plants found in asso- ciation in these beds, both as regards species and individuals, still belonged to lower Mesozoic types, such as ferns, cycads, and conifers, 206 F. H. KNOWLTON we find ancient if not really ancestral angiosperms, and many of the same types are found in beds of approximately the same age (that is Albian) at Circal in Portugal. Although we are here much nearer the origin of the angiosperms than was before known, we are proba- bly still some distance from their actual point of origin, but just where or when that was we do not, and may never know. No sooner were they fairly introduced, however, than they multi- plied with astonishing rapidity and in the upper members of the Poto- mac series—Raritan—they had become dominant, the ferns and cycads having mostly disappeared and the conifers having taken a subordinate position. By the close of the Comanchan, or Lower Cretaceous, they had spread as far north as Alaska and Greenland, and a large number of modern genera were established. ~* Climatic conditions during Comanchan.—The climate over this vast area was certainly much milder than at the present time, for such well-known plants as elms, oaks, maples, magnolias, and many others were growing 72° N., in Greenland and nearly as far north in Alaska. It was at least what we would now call warm temperate. U pper Cretaceous.—With the inauguration of the Upper Cretace- ous the angiospermous flora was in full swing. On the Atlantic border we have the Magothy, which extended from Maryland over New York, Long Island, and as far as Martha’s Vine- yard. The flora is a rich one, embracing about one hundred and fifty species. In the interior, in approximately the same position, is the Dakota, which has afforded a splendid flora of over five hundred species, and occurs in Kansas, Nebraska, Wyoming, Minnesota, along the inter- national boundary, and some of the same forms as far as central Alaska and south to Argentina. Of the succeeding members of the Upper Cretaceous the Colorado being largely marine has but a small flora, although in southwestern Wyoming there is a small flora, made up mainly of modern types of ferns (Gleichenia), that finds its closest affinity in the Upper Creta- ceous of Greenland. Montana.—As this represents alternations of marine with brackish- and fresh-water conditions we have a larger flora, although the total MESOZOIC AND TERTIARY FLORAS 207 number of known species probably does not exceed one hundred and fifty. Nothing particularly new was established at this time, the genera there being largely of older formations, though the species are mainly different. Laramie.—As the uppermost member of the conformable Cre- taceous series above the marine Fox Hills, the Laramie has had many vicissitudes of interpretation and was made to include beds now known to belong to the Montana, Arapahoe, Denver, Fort Union, etc. As logically restricted to the original definition of King, the plant-bearing Laramie is confined largely to the Denver Basin of Colorado and adjacent areas to the southward, with the probability of its being demonstrated to exist west of the mountains in Colorado, Wyoming, and New Mexico. As above restricted the Laramie flora comprises about one hundred and twenty-five species, and proves to be remarkably distinct from that of the Montana below as well as from the Arapahoe, Denver, and Fort Union above. Tertiary.—The close of the Upper Cretaceous saw a considerable percentage of the modern angiospermous types of vegetation fully established, not only in North America but throughout the world, and the ferns, cycads, and conifers relegated permanently to a sub- ordinate position. Certain types of dicotyledons, such, for instance, as magnolias, tulip-trees, sassafras trees, etc., had their maximum development in the Cretaceous, and in the Eocene and subsequent stages were greatly reduced until in the modern flora they are often represented by a few or even a single species of very restricted habitat. The most noticeable feature of the Eocene flora, broadly considered, is the increased number of forms that foreshadow the modern flora, a few, indeed, being still living. As examples of the latter mention may be made of the common sensitive fern (Onoclea) and two species of hazelnut (Corylus) all of which are now living in eastern North America. In late Cretaceous time the sedges (Cyperus, Carex, etc.) and grasses (Arundo, Phragmites) had but a poor representation, but in the late Eocene these groups clearly became more numerously developed both in types and species, and thus apparently made possible the rise and development of the mammalia. Fort Union flora.—The largest and in many respects most impor- tant Eocene flora is that of the Fort Union, which is found over a vast 208 F. H. KNOWLTON area in the central Canadian provinces, north as far as the valley of the Mackenzie River, and south over central and eastern Montana, the western portions of both North and South Dakota, and at many points in eastern and central Wyoming and northwestern Colorado. It has recently been shown by the writer! that the Fort Union, exten- sive as it was known to be, really embraces more than has commonly been assigned to it. Conformably underlying the beds by some geologists considered as the true Fort Union, occur beds which have often been incorrectly referred to the Laramie, or its equivalents, but which are now regarded as constituting the lower member of the Fort Union formation. This lower member, which includes the so-called “Hell Creek beds’? and “somber beds’? of Montana, and the “Ceratops beds” of Wyoming, and their equivalents throughout much of the area above outlined, contains a rich flora which is inseparably bound to the flora of the upper member. The flora of the Fort Union considered as a whole embraces more than five hundred species, and comprises ferns, sequoias, cedars, yews, grasses, sedges, oaks, willows, poplars in great abundance and variety, hazelnuts, walnuts, elms, sycamores, maples, a few figs, an occasional palm, and other more modern types. Whatever the con- ditions under which this flora grew and was entombed, it is beyond question that the climatic conditions were very different from those now prevailing in the region. But for the presence of palms and an occasional fig it might be presumed that the conditions were not greatly different from those now experienced in Atlantic North Amer- ica, that is, cool temperate. This flora, which is closely similar to that in north Greenland and the valley of the Mackenzie River, undoubtedly approached from the north. The presence of palms, which are found in the lower parts of the formation, argues, on the basis of present distribution, a somewhat warmer climate, just as the numerous thick beds of lignite throughout the formation argue for extensive, long-continued, moister, marsh conditions. The flora of the lower member of the Fort Union as at present elaborated embraces about eighty-five named species of which number about sixty-five are found in the upper member, while only sixteen of the eighty-five species are found in the Cretaceous below. t Proc. Wash. Acad. Sct., Vol. XI, 1909, pp. 179-238. MESOZOIC AND TERTIARY FLORAS 209 The unconformity of the base of these beds together with the differ- ences in the flora, clearly and logically marks the point at which the line is to be drawn between Cretaceous and Tertiary. In the Mississippian region in Louisiana and Mississippi we have a small Eocene flora (Eolignitic) comprising palms, evergreen oaks, magnolias, laurels, cinnamomums, etc., which appear to be most closely affiliated with small floras in northern New Mexico and adja- cent Colorado, the latter in turn being most closely related to much larger post-Laramie floras in the Denver Basin of Colorado. These embrace the Arapahoe with about thirty species, and the Denver with nearly two hundred species, and are believed to be slightly older than the Fort Union—in any event, there are only about thirty species in common. The Green River formation of upper Eocene age occupies a quite extensive area in central and western Wyoming, and has afforded a flora of some eighty species. It is very distinct from the Fort Union and other Lower Eocene floras, and shows a distinct increase of modern forms. In the northern Pacific coast region there are a number of Eocene floras, among them that of the Swauk which occurs just east of the Cascade Mountains in Washington. This large flora is entirely different from any other in this country, and consists of types that are for the most part found in Central and northern South America, among them being palms 6 feet in diameter and in layers sometimes a foot in thickness. This shows that the palms were not sporadic or occasional, and indicates, as do many of the other things, that the climate was mild, probably subtropical. The overlying Roslin for- mation contains a flora that is almost entirely different from that of the Swauk, and lacking the presence of palms was probably slightly cooler than the underlying formation. To the northward and covering a vast area in Alaska and well out on the Alaskan peninsula is the Upper Eocene Kenai formation which has afforded a rich flora of oaks, poplars, willows, hazels, walnuts, magnolias, horse-chestnuts, and maples, together with pines, spruces, cedars, and sequoias. This flora is found in British Columbia, and abundantly in Greenland, Iceland, and Spitzbergen, showing that it was of wide extent in similar northern latitudes. It is distinctly a 210 F. H. KNOWLTON warm-temperate flora. Another Upper Eocene flora is found in the Clarno formation of the John Day Basin, Oregon, and in the Payette formation of western Idaho. It embraces walnuts, hazels, birches, alders, oaks, elms, sycamores, maples, ashes, etc., and is temperate or warm temperate, in character. Eocene floras in the Atlantic area are of very little importance as thus far developed. Miocene.—The Miocene flora of North America is relatively not a large one although it comprises probably five hundred species as now known. The deposits occur often in isolated basins, widely separated, and there is usually comparatively little in common between them. A number of the more important areas may be briefly mentioned. At Brandon, Vermont, in the midst of ancient crystalline rocks, occur small pocket-like deposits of lignite which have yielded large numbers of fossil fruits and a very few poorly preserved leaves. The fruits have been studied by Lesquereux, Perkins, and others, and about one hundred and fifty nominal species described belonging to the genera Nyssa, Hicoria, Juglans, Bicarpellites, Cucumites, Tri- car pellites, etc. At Florissant, Colorado, also in the midst of older rocks, there are small lake-bed deposits which have afforded vast quantities of plant and insect material in an admirable state of preservation. The plants number upward of two hundred species, among them being a great number of very modern types and even including not a few herbaceous forms. This flora as a whole is very unlike anything found in the region at the present day and apparently finds its closest affinity with the West Indies, though doubtless it also approached originally from the north. Small deposits containing a Miocene flora have been found in Esmeralda County, Nevada, the Similkameen Valley, and other points in British Columbia, and in the Yellowstone National Park. The so-called Muscall beds of the John Day Basin, Oregon, and extending into central Washington, have yielded a rich flora of about eighty species, among them oaks, maples, poplars, barberry, bread- fruit trees, etc., indicating a warm, moist climate. Associated with the auriferous gravels of California is a flora of about one hundred MESOZOIC AND TERTIARY FLORAS Ari and twenty-five species, some of which are of very modern appear- ance, such as Zizyphus, Magnolia, Persea, Acer, Artocar pus, etc. Pliocene.—The Pliocene flora of North America is almost a negli- gible quantity, about the only known locality being the Falls of the Columbia River. It includes species in the genera Woodwardia, Sassajras,Sterculia, etc., and is very closely related to living American species. Pleistocene.—The Pleistocene flora is better known than the last, yet we are undoubtedly only on the borderland of a knowledge of the plants of this period and their distribution. Small Pleistocene floras are known from New Jersey, Maryland, Virginia, West Virginia, North Carolina, Alabama, New York, Iowa, and Canada. The most extensive exploitation of this flora is that made in Canada in the vicinity of Montreal and Toronto, where Penhallow has been able to make out at least three stages. The species are nearly all living. CHAPTER od CONDITIONS GOVERNING THE EVOLUTION AND DISTRI- BUTION OF TERTIARY FAUNAS? W. H. DALL U. S. National Museum, Washington D. C. The subject allotted me being “The Conditions Governing the Evolution and Distribution of Tertiary Faunas,” I may begin by stating certain propositions which, for the purposes of this discourse, may be assumed as axiomatic. t. A fauna is an assemblage of organic species populating a given area at one and the same epoch, and—allowances being made for the preferences of such minor groups as carnivorous, phytophagous, littoral, benthal, petricoline, and limicoline animals—having for the most part identical geographical distribution. 2. We may regard it as indisputable that the properties of the environment shown to influence a living fauna, or to control its distri- bution, were capable in Tertiary? times of exerting an analogous influence on faunas now known chiefly by their fossil remains; and, conversely, if in a fossil fauna we are able to trace certain definite features, which in a living assembly would result from a particular environment, we are justified in concluding that the fossil fauna in question was, when living, subject to the action of an analogous environment. To illustrate this second proposition it may be said that if fig trees can now flourish and reproduce their species only in regions having a mean minimum temperature of thirty degrees Fahrenheit, and a summer mean temperature of not less than sixty degrees; and, secondly, if we find in the Tertiary leaf-beds of Greenland and Spitsbergen indications of groves of fig trees having flourished there in the Oligocene epoch; then we are likewise justified in assuming 1 Published by permission of the Director of the U. S. Geological Survey. 2 The author realizes that these factors may not be entirely applicable to the faunas of pre-Tertiary epochs. EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 213 that in Greenland at that epoch the summer mean temperature did not fall far below sixty degrees, nor the winter cold maintain itself greatly below the minimum above mentioned. Among marine animals a consensus of the evidence on record points insistently to temperature as the most important factor in determining the existence and persistence of species in a given area; and the toleration oi an organism and its progeny for fluctuations of temperature limits its geographical distribution as positively as would a material barrier. In the absence of such mortal extremes of temperature, material barriers, unless hermetically complete, really count for very little in determining distribution. In utilizing fossil faunas as chronologic indicators of geologic time, the marine faunas are more readily utilized for the grand divisions of the scale than the land faunas, especially when the latter are characterized chiefly by fossil vertebrates. This is because the marine conditions are more uniform, less affected by meteorologic factors, and more dependent upon conditions which affect the whole hydrosphere rather than small areas of it. The struggle for life is less intense, the food supply generally more adequate, enemies less vigorous, and dangerous fluctuations of temperature far less frequent, in the sea than on land. The same features make the land faunas more clearly indicative of minor divisions of the scale, and of the progress of organic evolu- tion in the general region concerned; while less conclusive as to the contemporaneity of widely separated though analogous faunas. The lability to sudden extermination by epidemic diseases, or by sharp meteorologic changes of very short duration, or even by the incursion of multitudes of small enemies, insects, or carnivora injuri- ous to the young, is vastly greater among the land vertebrates than among marine animals. Marine vertebrates are more subject to injury from temporary causes than are the invertebrates associated with them. A marked instance of this was the destruction of the “‘tilefish” of the middle Atlantic coast a quarter of a century ago, if the explanation finally accepted as most probable by Professor Baird and other experts be the true one. The “tilefish” inhabited a region where the water, warmed by the proximity of the Gulf Stream, was of a moderate temperature. The combination of violent 214 W. H. DALL winds from a quarter which led to the forcing to the eastward of the Gulf Stream water, and to the influx of much colder water from the Polar current into the area thus vacated, was believed to be respon- sible for the almost total extermination of these fishes, which were found floating dead and apparently uninjured in millions on the surface of the sea, by navigators bound into New York and adjacent ports. This temperature change which lasted at most for a few weeks would probably have had no effect whatever on the adult larger invertebrates of the same area, though to any of their larval young it might well have proved fatal. Another season would replace these, but the restocking of the fauna with “tilefish,” which finally took place, required many years. A statement of the factors which are regarded as modifying existing marine invertebrate faunas will put the student in possession of the chief factors which may have affected analogous faunas during past geologic time. My point of view is that afforded by a knowledge of conditions affecting molluscan life. Census oj species—From a discussion too long to quote here in full,t I have drawn the following conclusions: That the part of the average mollusk-fauna which is capable of leaving traces in the shape of fossils, under conditions not greatly differing from those of the present day, in a region where the temperature of the sea ranges during the coldest winter month between 32° and 4o° F. (which might be called boreal), would comprise about 250 species. In case the temperature ranged between 40° and 60° (cool temperate) about 400 species might be expected. With a range between 60° and 70° (warm temperate) we should find about 500 species, and in the tropical zone (70° to 80° F.) not less than 600 species; and in specially fa- vorable localities of the tropics nearly twice as many. Learning from the characteristic genera what zone of temperature a given fauna may have belonged to, we can with confidence predict approximately the number of species which it will prove to contain when fully explored. Of course in a single locality where the char- acteristic situs is exclusively mud, or rock, or fine sand, only a certain t Bull. U. S. Geological Survey, No. 84, Correlation Papers, Neocene, 1892, pp. 25-28. EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 215 proportion of the total fauna will be represented, but these minor groups are not entitled to the designation of a fauna as used in this paper. Relations of temperature to the jauna.—In considering the relations of temperature of the water to the fauna, account must be taken of the vertical differences. ‘The temperature of the water at the surface differs materially from that at the bottom in most regions, where the depth is over a few fathoms. Arctic or Antarctic species may extend in cold depths of ocean for thousands of miles; while, in the warm superficial strata above them and inshore from them, a totally different assembly lives and thrives. It is easy, in the case of widely diffused northern species, when deep water dredgings have revealed the distri- bution, to observe in the tables the boreal forms descending with the temperatures to deeper and deeper water as they approach the tropics. That this is so generally true is satisfactory evidence that the factor of pressure, being equalized by thorough permeation of the organism, is less effective in limiting distribution than most other factors. It seems incredible that the large eggs of abyssal mollusks can go through the processes of development under a pressure of tons to the square inch; since there must be a limit somewhere to the permeability of tissues. Still it is evident that they do. Why temperature should be so important in limiting distribution is a question which may be answered in several ways. Brooks has shown that, while the embryonic oysters (Ostrea virginica) are swim- ming at the surface of the sea, an entire brood may be destroyed to the last individual, bya fall in temperature of a few degrees, due toa cold rain. While it is not improbable that oysters from the northern part of the range of the species, say Nova Scotia, may have in the embry- onic state a greater tolerance for a fall in temperature than those of a relatively warmer region like Chesapeake Bay or the coast of Florida, yet it seems likely that a certain narrow range of temperature is required for the developmental stages, and that the distribution of the species is limited to the area where such temperatures may be had during the spawning season. Thus, for example, young Chesapeake oysters of an inch and a half in breadth may be transported to the Pacific coast, planted in suitable locations, and will flourish well, growing even faster than in 216 Weil DALE their native waters. Yet of the billions of spat which these oysters have discharged into the waters of the Pacific (fifteen or twenty degrees colder than the Chesapeake at spawning time) there is not a trace left in the shape of young oysters. In spite of the best efforts of the local oystermen the Chesapeake oyster has not become accli- mated. Another way in which temperature may affect a fauna is in pro- moting or inhibiting the minute plant-life which forms the food of many bivalves. In all cases it is certain that a fall below a certain level of temperature is more effective upon the animals subjected to it than a corresponding rise in temperature. The first, as I have indicated, may kill; the second, merely accelerate development. The very low temperatures nearly universal on the floor of the open ocean, and the otherwise uniform conditions that prevail there, offer favorable opportunities for wide distribution of boreal organisms. I am informed by Mr. A. H. Clark that the Antarctic Crinoidea, characterized by scaly segments, have penetrated by this road in the Eastern Pacific even to the Oregonian region; while on the opposite coast the smooth-segmented Arctic forms have been traced far to the southward. As indicators of subaerial conditions it is obvious that littoral invertebrates are more useful than those of deeper waters, since they are more exposed to climatic changes. It may happen that a vertical section of the submarine continental slope drawn at right angles to the coast from the shore to the oceanic floor may, and in most cases will, cut through a series of different faunas corresponding to the temperatures encountered. Off Cape Hatteras the cold inshore current from the north is the haunt of a cool-temperate fauna with some boreal elements. Thirty miles off shore, in less than fifty fathoms, the fringe of the Gulf Stream protects a fauna in large part identical with that which characterizes the Bahama Banks and Bermuda. ‘The large species of Venus, which penetrated to the north shore of the Gulf of Mexico with the cool Miocene water, have maintained themselves notwithstanding the subsequent rise of tem- perature and persist in these new conditions to the present day, a notable example of adaptation. On the other hand the subtropical Rangia and Corbicula, which advanced with the warm Pliocene waters EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 217 far to the north of their original station, have left only sparsely scat- tered fossils as an indication of their invasion. In the later Tertiaries the proportion of recent species is sufficient, taking into account the present distribution of these species, to afford the means for a very probable estimate of the temperature which prevailed during the particular portion of Tertiary time when they formed part of the fauna. An interesting example of this is afforded by a small collection of fossils obtained by Stimpson in 1865, from above the lignitic coal measures in the northeast angle of the Okhotsk Sea, in Penjinsk Gulf.t | I have reported in full upon these fossils, and it is sufficient to say on this occasion that the climate and recent fauna of the locality are Arctic and the open water of the sea persists only for some three months of the year, while the species of fossils indicate that during their existence in the living state the annual mean air temperature, at the most moderate estimate, must have been 30° to 40° F. warmer than at present. Another instance has recently been brought to my attention. During the two seasons just past, collections have been made from the Pliocene auriferous gravels of the coast of Alaska near the town of Nome.?_ Thirty-three species have been identified of which seven appear to be new, eleven are now known living only south of the line of floating ice in winter, one is a Miocene species, and the remaining fourteen are common to the Alaskan fauna in general from the Arctic to British Columbia. This indicates clearly that during the Pliocene, when these gravels were being laid down, the climate of Norton Sound, now subarctic, was not colder than that of North Japan or the Aleutian Islands where the sea remains unfrozen throughout the entire year. This agrees well with the evidence from the marine Pliocene of the northeastern corner of Iceland, which has afforded over one hundred species, of which seventy-four are said to be common to the Crag fauna of the British Islands, corresponding to an annual mean air temperature not lower than 42° F., while it is hardly necessary to say that the present t Proc. U. S. Nat. Mus., Vol. XVI, No. 946, 1893, pp. 471-78, pl. LVI. The age of the fossil shells in the report upon these fossils was given as Miocene, but it is probable that like the analogous lignite deposits of the adjacent shores of America, the underlying coal measures may be referable to the Upper Eocene or Oligocene and may have been laid down contemporaneously with the American Kenai formation. 2 Cf. Am. Jour. Science, Vol. XXIII, June, 1907, pp. 457, 458. 218 We DALE conditions in north Iceland are purely Arctic. A little patch of Pliocene at Gay Head, Mass., afforded a fragment of the genus Corbicula, now warm temperate in its distribution; while the older of the deposits at Sankoty Head, Nantucket, as well as those at Nome, show that some of the species which ranged at that period from Bering Sea to the North Atlantic are now strictly confined to temperate waters in their respective hemispheres. I have given most of my time to the relations of temperature to faunas, as this is the most important, pervasive, and obvious factor of the modifying environment, but there are a few others which may be briefly alluded to. The question of food is next in importance to temperature. It is true that the ocean almost everywhere is a generous provider for its inhabitants, so that only special scrutiny reveals important differences in the food supply, a large part of which is furnished by almost microscopic animals. Yet it has been conclusively shown that in places where a persistent movement brings constantly fresh supplies of food and well-aerated water, as on the continental slope washed by the Gulf Stream, or where the periodical ebb and flow of the tides do the same thing on a smaller scale—there the oceanic population flourishes with especial vigor and abundance. Near the shores a special quota of plant-feeders live, in their turn furnishing provender for carnivorous species. ‘The distribution of plant food in the shape of algae thus governs the distribution of the phytophagous species. We find on the basalts, andesites, and recent lavas of the Aleutian chain of islands, enormous groves of kelp and meadows of olivaceous rock-weed. Whether because of something in the chemical com- position of these rocks, or otherwise, the red and green seaweeds are almost wholly absent from them. However, where the granitic masses which form the core of some of the islands (and in other places stand alone, domelike in the sea) are within reach of the waves, we find a special flora of the more bright-colored algae and a special fauna dependent upon them. No matter how isolated the patch of granite, the characteristic animals recur, and in many cases reproduce in their own tints the rosy hue of the plants upon which they depend for food. In the abysses where the absence of sunlight excludes plant life EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 219 the animals are almost exclusively carnivorous and largely subsist on the abundant rain of dead organisms which slowly descends from the surface layers of the sea. It has been customary to regard the 1oo-fathom line as constituting a sort of boundary between the fauna of the shores and of the deeps. This has a certain foundation in the fact that at greater depths no living algae can exist for want of sunlight. A more or less constant migration, casual or accidental, is constantly taking place between the littoral region and the deeps, but it is so slow, and the process of adaptation to the new conditions so gradual, that we may safely regard the abyssal fauna as even geologically old. I have called attention to certain features of the eastern Pacific and Antillean abyssal faunas which illustrate these remarks in the introduction to a recent monograph." Freshwater and terrestrial invertebrates are subject not infre- quently to one set of influences which is rarely noticed in the open sea. This is, in the case of the limnophilous species, a change in the mineral content of the water in which they live. ‘This is usually gradual and when injurious chiefly due to the concentration of salts (which exist in all freshwaters arising from drainage) by evaporation. In the case of many large Pleistocene lakes, of which the prehistoric Lake Bonneville may be taken as an example, this process has been carried on until the saline content of the water became so excessive that all molluscan life became extinct, as in the Great Salt Lake of Utah. A careful study of the beds of shell-marl deposited by the shrinking lake shows that the effect of the gradually increasing salinity of the water on the freshwater mollusks contained in it was to lead to a thickening and corrugation of the shell, a tendency to longitudinal ribbing, and a diminution in average size, all of which changes may perhaps be due directly to the astringent action of the salts of sodium and magnesium upon the thin and delicate margin of the mantle which secretes the additions to the shell. These char- acteristics become more and more pronounced as the waters become more saline, until finally the conditions become too rigorous for survival. The gradually intensified effect of the increase of salinity may be beautifully illustrated by a collection of the fossil shells from 1 Bull. Mus. Comp. Zoblogy, Vol. XLIII, No. 6, October, 1908, pp. 205-12. 220 W. 1. DALL the successive marl beds around Great Salt Lake. Another instance, probably of the same nature, is afforded by the marls of Steinheim, in Wurtemburg, of which the mutations shown by the species of Planorbis, in particular, are described in the well-known monograph by Hyatt.” A somewhat similar effect seems to be produced in the case of landshells inhabiting arid volcanic islands in windy regions. Here the astringent effect appears to be produced by the alkaline volcanic dust to which these animals living on almost bare shrubs or among sparse herbage are more or less constantly exposed. I have called attention to the conditions under which this effect seems to be pro- duced in a paper on the landshell fauna of the Galapagos Islands.’ This illustrates how upon animals of quite different systematic rela- tions, similar effects, simulating an apparent convergence, may be caused by the direct action of the environment upon individuals. Paleontologically these instances are worth noting, as otherwise the forms concerned might well be regarded as belonging to totally dif- ferent groups from the individuals which developed normally in an ordinary habitat. In conclusion I may call attention to certain factors which have serious importance in modifying the fauna of a large extent of coast catastrophically, and which inferentially are to some extent responsible for the marked changes we observe in different stratigraphic horizons where we do not find indications of coincident orogenic changes. In some regions, as the west coast of the Floridian peninsula, the strata may be slightly inclined so that the beds between which sub- terranean waters move have their edges beneath the sea. ‘Torrential rains in the interior of the peninsula carry vegetable matter into the interstices of the soft limestone rocks, where it decays with the accom- panying production of carbon dioxide and sulphuretted hydrogen gas. This accumulates and under the hydrostatic pressure of an excep- tionally heavy rainfall is sometimes forced out beneath the sea from the edges of the submerged strata in sufficient volume to kill by suffo- 1 “ Genesis of the Tertiary Species of Planorbis at Steinheim,” Anniv. Mem. Boston Soc. Nat. History, 1880, pp. 114, pls. I-IX, 4to. 2 “Insular Landshell Faunas, Especially as Illustrated by the collection of Dr. G. Baur on the Galapagos Islands,”’ Proc. Acad. Nat. Sciences, Philadelphia, August, 1896, DP: 395 459- EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 221 cation every living thing along many miles of coast. This has happened on the coast of Florida several times within my recollection. The repopulation of the devastated area is slow and can rarely reproduce exactly the same assemblage of animals which previously occupied that area. Another mode in which widespread extermination of a sedentary population of invertebrates may be brought about is by the sudden appearance of vast multitudes of minute organisms like Peredinia. Within the last few years, both on the coasts of Japan and of Cali- fornia, the sea at times has been covered for miles with reddish clouds of these submicroscopic creatures. On their advent near the shore, driven by wind or currents, the shellfish, corals, and fishes are rapidly suffocated, and, if the pest continues, everything within the area it occupies will succumb. I have heard that, within two years, the Japanese pearlshell preserves on the seashore of that country have been almost wholly ruined by the organisms referred to, with the loss of hundreds of thousands of dollars, to say nothing of years of labor rendered fruitless. PALEOGEOGRAPHIC MAPS DERTIARY BAILEY WILLIS U. S. Geological Survey I3 AND 14. EOCENE-OLIGOCENE AND MIOCENE The Eocene-Oligocene aspect of North America differed from the Cretaceous and resembled the present. The east and west were united. The Cordillera had begun its development as a system of many mountain chains, most, if not all, of which are represented in existing ranges; yet few, if any, of which have had an uninterrupted growth. They became high in the Eocene, but were greatly eroded in the Oligocene and Miocene. The volcanic activity which marks the Cordillera was very notable during the Eocene. The eastern part of the continent remained low. By erosion of the mountains and by contributions from the volcanoes great thicknesses of sediment accumulated in interior basins of the Cordillera. The deposits were in part fluviatile, in part eolian, in minor part lacustrine. On the map their distribution is shown by the ruling for continental deposits in the central west. In the Gulf region and also in Alaska extensive low lands and favorable climate produced extensive marshes which are now repre- sented by coal beds and are also indicated by the vertical ruling. The continental connections of North America during the Eocene and Oligocene appear to have been established and interrupted, as is shown by the relations of land animals. Osborn infers that there was intermigration with Europe during the Wasatch epoch, and thenceforward separation from Europe until the Oligocene, when faunistic reunion took place. ‘These inferences are suggested on the map by the temporary lands linking Alaska with Siberia and Green- land with England. The region of the West Indies was the seat of an embayment of t Osborn, H. F., ‘‘Cenozoic Mammal Horizons of Western North America,” U. S. Geological Survey Bull. 361, 1909. 222 PALEOGEOGRAPHIC MAPS 22 ios) I i i Tt * 20 -—— NORTH AMERICA . OcEANIC BASINS RRR MARINE WATERS (EPICONTINENTALI) SEA OR LAND, MORE LIKELY SEA LAND OR SEA, MORE LIKELY LAND LANDS INDETERMINATE AREAS POLAR CONTINENTAL DEPOSITS, SOMETIMES EQUATORIAL = _sINCLUDING MARINE SEDIMENTS ED 10" 100 30* MARINE CURRENTS BAILEY WILLIS N N | | | I | MERICA ORTH A N LEGEND SINS NIC BA OCEA MARINE WATERS (EPICONTINENTAL) MORE LIKELY SEA D EA EA OR LA s MORE LIKELY LAND s LAND OR Ss TEMPOR LAND ARY SOMETIME CONTINENTAL DEPOSITS, POLAR ARINE CURRENTS M EQUATORIAL s INCLUDING MARINE SEDIMENT ¥ LAND Ti0® PALEOGEOGRAPHIC MAPS 22 cn the Atlantic, beneath which was deposited the widespread Oligocene limestone, characterized by the faunas of a warm oceanic current. This fauna spread north along the southeastern coast of the United States. I am indebted to Dr. Wm. H. Dall and Dr. Ralph Arnold for discussion of the distribution of marine faunas and their relation to inferred currents. In outline, North America during the Miocene resembled the continent during the Eocene. The surface was, however, less mountainous. The sites of the Sierra Nevada and of the Coast Range of British Columbia were plains or low hilly lands. The Rocky Mountains of the United States were comparatively low. In British Columbia, and thence southward through Washington, Oregon, and Nevada occurred outflows of lava, which covered many thousand square miles, but which in general were not from volcanoes. ‘Though probably subordinate in volume of lava erupted, volcanoes were numerous and they gave off quantities of volcanic ash, which formed deposits in lakes, particularly in western Montana and British Columbia. The elevation of the Rocky Mountains of western Montana and British Columbia by overthrust, and subsequently the development of longitudinal valleys and separate ranges by vertical displacements, probably began in the Miocene period and may have culminated dur- ing Pliocene or early Quaternary time. In the West Indian region the close of the Oligocene period was marked by a notable disturbance, which raised a folded mountain chain from Puerto Rico to Cuba and probably continuously to Yucatan. It may also have closed the Isthmus of Tehuantepec and possibly have temporarily connected Honduras with South America. Another possible line of connection is around the eastern end of the Caribbean through the Windward Islands. If, however, such a land link united North and South America it was but temporary. The effect of the Cuban elevation, or of some other geographic change not yet suggested, was to shut off from the northern Gulf and southern Atlantic coasts the warm currents which had sustained a rich southern fauna and to admit the cool northern waters with their appropriate life. A very pronounced faunal change, without any marked stratigraphic break in the sediments, was the result. CHART HRe aim ENVIRONMENT OF THE TERTIARY FAUNAS OF THE PACIFIC COASTSOF THE UNEEED STALES: RALPH ARNOLD CONTENTS INTRODUCTION CORRELATION TABLE ACKNOWLEDGMENTS THE EocENE PERIOD Relation of the Eocene to the Cretaceous Conditions immediately preceding and inaugurating the Eocene Distribution and character of sediments Conditions prevailing during the Eocene Orogenic movements and volcanic activity in the Eocene Climate during the Eocene THE OLIGOCENE PERIOD The Oligocene a period of elevation Conditions of erosion and deposition Fauna and climate of the Oligocene THE LOWER MIOCENE PERIOD Conditions inaugurating the lower Miocene Distribution and character of sediments Conditions of deposition Volcanic activity in the lower Miocene Faunas and climate of the lower Miocene Period of diastrophism in the middle Miocene THE Upper MIOCENE PERIOD Distribution and conditions of deposition Erosion and volcanic activity Faunas and climate of the upper Miocene THE PLIOCENE AND QUATERNARY PERIODS Conditions of deposition and character of sediments Diastrophism and volcanism in the Pliocene Diastrophism in the Quaternary Faunas and climate of the Pliocene and Pleistocene 1 Published by permission of the Director of the U. S. Geological Survey. 226 TERTIARY FAUNAS OF THE PACIFIC COAST bo bo Sy SUMMARY AND CONCLUSIONS Summary Cycles of diastrophism Periods of maximum elevation and subsidence Changes in climate Diastrophic provinces INTRODUCTION This paper was presented as part of the symposium on “ Correla- tion” arranged by Mr. Bailey Willis as the principal subject for discussion in Section E of the American Association for the Advance- ment of Science, and later continued as the main feature of a special section of the Geological Society of America, at Baltimore during Convocation Week, 1908. The paper treats in a general way of the character and distribution of the sediments laid down, and the faunas and the conditions prevailing during the Tertiary period on the Pacific Coast of North America, more especially that portion lying between Puget Sound on the north and the Gulf of California on the south. The discussion is also restricted almost exclusively to the territory directly affected by the sea, as a detailed consideration of the conditions and faunas prevailing inland belongs more properly within the province of the paleobotanist and vertebrate paleontologist. Special attention is called at several places throughout the discussion to the extraordinary localization of many of the earth-movements affecting the region under discussion and the writer wishes to advance this localization of phenomena as an argument against the too free use of diastrophism, unsupported by paleontologic evidence, as a basis of correlation. The preparation of the paper has necessitated the correlation of the various Tertiary formations of the Pacific Coast—in fact the paper is obviously based on these correlations—and for that reason a general table of correlation is here included for reference. Lack of space prevents a discussion of the reasons for many of these correlations. Some of them differ from those previously published by the writer,’ but for the most part they are those usually accepted by West Ameri- can geologists and paleontologists. 1 Jour. Geol., Vol. X, 1902, p. 137; Mem. Cal. Acad. Sci., Vol. III, 1903, p. 13; U. S. Geological Survey Prof. Paper 47, 1906, p. 10; U.S. Geol. Survey Bull. 309, 1907, P- 143; tbid., 321, 1907, p. 21; ibid., 322, 1908, p. 27. 228 RALPH ARNOLD The fourfold subdivision of the Tertiary is the one which seems best to fit the phenomena of the Pacific Coast, although for con- venience of discussion in the present paper the writer has separated the upper from the lower Miocene on account of the diverse geologic histories of the two. It is obviously impossible to make exact correla- tions between the European and East American subdivisions on the one hand and the faunal and stratigraphic subdivisions of the Pacific Coast on the other, but by means of various direct and indirect methods it is possible, however, to make approximate correlations, and as the work progresses these approximations will be made to approach nearer and nearer to the exact. Paleontology forms the basis for the correlations, but other criteria, such as periods of wide- spread diastrophism and volcanic activity and profound changes in climate, have also been taken into consideration. It is well to men- tion here that the total thickness of Tertiary and Quaternary sedi- ments in California approximates 25,000 feet and that within the Tertiary and Quaternary periods, relatively short, geologically speaking, as compared with the earlier divisions of the time scale, probably more distinct and profound movements have taken place on the western border of our continent than have occurred over an equal length of time in any of the preceding periods within the limits of North America. Five maps have been prepared to elucidate the paper, each respec- tively representing the supposed distribution of land and water along the western border of the United States during the Eocene, the Oligocene, the lower Miocene, the upper Miocene, and the Pliocene and Pleistocene epochs. It is admitted that these maps are composites; that is, they represent the distribution not at any definite moment but throughout a period of time during which the local conditions usually changed but little relative to the changes taking place between these periods. For instance, the areas shown as subject to deposi- tion during the Eocene are the areas over which deposits were laid down at one time or another during the Eocene epoch. In the case of certain portions of Puget Sound and elsewhere, marine conditions prevailed during the early Eocene, brackish-water conditions a little later, and freshwater or river, and coal-marsh conditions toward the close. In other portions of the same general area the conditions TERTIARY FAUNAS OF THE PACIFIC COAST 2209 alternated. It is obvious, therefore, that the legends on the maps are very general. Only in those instances where the body of water indicated as fresh remained fresh throughout practically the whole of its existence is it indicated as a freshwater area on the map. The periods chosen for representation and as units for discussion are neither of equal length nor of equal importance, and the lines separating them are in some instances arbitrary; but it is believed that they serve the purpose of systematizing the discussion better than any other plan of subdivision. The data are incomplete and the conclusions admittedly tentative, and it is expected that future investigations will disclose new and important information, which will necessitate alterations, but the fact remains that general reports of this kind, based as they are on the present state of our knowledge, often point the way to more exact results in the future. ACKNOWLEDGMENTS The writer wishes to acknowledge his indebtedness to Messrs. Bailey Willis, J. S. Diller, T. W. Stanton, Robert Anderson, Chester W. Washburne, and several others for personal assistance in the preparation of the text and maps, and to express his thanks for the services rendered. In addition to the personal aid received, the literature relating to the subject of West Coast geology has been freely drawn on in the compilation of relevant data and in many cases proper acknowledgment for this is made in the text. THE EOCENE PERIOD RELATION OF THE EOCENE TO THE CRETACEOUS Before entering into the details of the geologic history of the Tertiary it is well to consider for a moment the relations existing between the earliest Tertiary rocks and those of the Cretaceous, and to note the conditions initiating the Tertiary, as implied by these relations. A widespread unconformity exists between the Eocene and the Cretaceous on the Pacific Coast of North America. Throughout Washington, Oregon, and certain parts of California, this uncon- formity is angular, while over considerable areas in California and at one locality in Oregon the unconformity may only be recognized by a more or less marked hiatus in the faunas. 230 RALPH ARNOLD It is a noteworthy fact that with one exception wherever the line between the marine Eocene formations (Martinez, Arago, Tejon, etc.) and the Cretaceous beds is marked by an angular unconformity, the MARINE FRESHWATER i , i lh | = — SS = FF SS SOCeN Es. $=} Ralph Arncla, 19 — DN Fic. 1.—Map showing hypothetical distribution of land and water on the Pacific Coast of the United States during Eocene time. underlying beds are either of lower Cretaceous (Knoxville) or middle Cretaceous (Horsetown) age, and that wherever the Eocene rests on the Chico, or upper Cretaceous, ex- cluding the case at San Diego, the unconformity is not angular, and as far as the stratigraphic evidence goes, the two formations represent an apparently uninterrupted period of sedimentation. The apparent conformability of the Eocene on the Cretaceous, to- gether with the superficial similarity of their faunas, led Gabb and Whitney of the early California Survey to class the Martinez and Tejon formations with the Cre- White, Stanton, and Mer- riam have, however, shown the Eocene age of the Martinez and Tejon. Of the relationships existing between these two and the Chico, or upper Cretaceous, Dr. Merriam has the following to say: taceous. The Martinez group, comprising in the typical locality between one and two thousand feet of sandstones, shales, and glauconic sands, forms the lower part of a presumably conformable series, the upper portion of which is formed by the Tejon. It contains a known fauna of over sixty species, of which the greater portion is peculiar to itself. A number of its species range up into the Tejon and a very few long-lived forms are known to occur also in the Chico. Since the Martinez and Chico are faunally only distantly related it is probable that an unconformity exists between them.? t Jour. Geol., Vol. V, 1897, p. 775- TERTIARY FAUNAS OF THE PACIFIC COAST 231 Another fact showing the relations existing between the Eocene and the Cretaceous is the occurrence in the Eocene beds in the Rose- burg region, Ore., of oysters so similar in appearance to the character- istic Cretaceous fossil, Gryphea, that without their accompanying Eocene fauna these oysters would certainly be mistaken for Cretaceous forms. CONDITIONS IMMEDIATELY PRECEDING AND INAUGURATING THE EOCENE Immediately preceding the Eocene period practically all of Wash- ington, all of Oregon excepting a small area along its southern border, the Sierran and desert region, and certain portions of the coastal belt of California were dry land. Most areas in California, and possibly also those in the Puget Sound region, which were occupied by the Chico or upper Cretaceous sea, were still under water, or at least elevated only slightly above sea-level and this without deforma- tion of the Chico beds or subsequent erosion before subsidence. Influences, however, which markedly affected the faunas without materially influencing the sedimentation, were actively at work, and it seems likely that these influences were due to worldwide climatic changes augmented by a readjustment of ocean currents following orogenic movements. In Washington, according to G. O. Smith, the deposition of the Cretaceous rocks seems to have been followed by an epoch in which they and older rocks were folded and uplifted. Thus was an early Cascade Range outlined, although it may be that the range had an even earlier origin. Accompanying the post-Cretaceous mountain growth were intrusions of granitic and other igneous rocks which now constitute a large part of the northern Cascades. During the time that any portion of this area was not covered by water the rocks were exposed to the vigorous attacks of atmospheric agencies. Thus, at the beginning of the Tertiary the northern Cascade region appears to have been a comparatively rugged country, although not necessarily at a great elevation above sea-level. A study of the interrelations of the Cretaceous and Eocene forma- tions outlined in a preceding section clearly indicates that any impor- tant pre-Eocene mountain-building movements affecting the Creta- ceous rocks in the California province must have taken place before the deposition of the Chico or upper Cretaceous sediments. As shown by F. M. Anderson,? the movements immediately preceding “Ellensburg Folio,” Geol. Atlas U. S., No. 36, p. 1. 2 Proc. Cal. Acad. Sci., 3d ser., ‘“‘ Geology,” Vol. II, 1902, p. 53- 232 RALPH ARNOLD the deposition of the Chico were accompanied by basic igneous intrusions. No profound movements and no volcanic activity accompanied the post-Chico (post-Cretaceous) movements in Cali- fornia as they did in Washington. Steep mountains bordered the youthful Eocene sea in southern Oregon, northeastern California, and north of San Diego, and occupied portions of one or more large islands in the region of Mon- terey and Santa Barbara counties south of San Francisco. Elsewhere the relief of the land appears to have been comparatively low and the shore-lines with few bays or estuaries. DISTRIBUTION AND CHARACTER OF SEDIMENTS Rocks of marine origin and Eocene age are found at many local- ities throughout Washington and Oregon west of the Cascade Range, and over considerable areas of the Coast Ranges in central and southern California. Although Eocene rocks probably once fringed the greater part of the western base of the Sierra Nevada, they are now all removed by erosion or covered by later formations except at one locality near Merced Falls. For the most part the Eocene rocks of the Pacific Coast are either sandstone or shale. Conglomerate is found at the base of the formation throughout southeastern Oregon, north of San Diego, and at a few localities along the northeastern flanks of the Coast Range; and at Port Crescent, Washington, Eocene fossils are associated with tuff; but these occurrences are exceptional. Also, diatomaceous shales occur at the top of the Eocene series in the vicinity of Coalinga, Cal., where they are believed to be the source of important deposits of petroleum. Coal and other indications of shallow- and brackish-water conditions are found over much of Washington and Oregon and California, usually overlying marine Eocene beds. The maximum thickness of the Eocene sediments varies from 8,500 feet east of the Cascades,' 10,000 to 12,000 feet in western Oregon? to gooo+ feet in southern California. CONDITIONS PREVAILING DURING THE EOCENE During the early part of the Eocene, marine conditions prevailed over a considerable territory that later was covered by brackish- or 1G. O. Smith, Mt. Stewart Folio. 2 J.S. Diller, Roseburg, Coos Bay, and Port Orford Folios. 3 Ralph Arnold, U. S. Geol. Surv. Bull. 321, p. 21. TERTIARY FAUNAS OF THE PACIFIC COAST 233 freshwater or swamp conditions. The regions thus affected include a large part if not all of the Puget Sound and western Oregon provinces and a considerable part of central California. How far these condi- tions extended eastward into central Washington and Oregon it is not possible to state owing to the covering of the Eocene by later volcanic flows. It is quite possible, however, that certain portions of the Sound country was at no time submerged under salt water, or if at all only for very short periods, for Willis states' that coal occurs both in the basal and upper portions of the Puget formation, which is believed to cover the period from the Eocene into the Miocene. He states further that “the physical history which is recorded in the Puget formation is one of persistent but frequently interrupted sub- sidence” in which “the alternation of coal beds with deposits of fine shale and coarse sandstone indicates that during this great sub- sidence the depth of water frequently changed.’ He infers “that at times the subsidence proceeded more rapidly, and that the deepened water was then filled with sediment, until the tide-swept flats became marshes, and for a time vegetation flourished vigorously in the moist lowlands,” this rotation being repeated intermittently. This description of conditions is believed also to apply to much of Alaska, western Oregon, and portions of the interior valley of central Cali- fornia during the later Eocene. The epicontinental Eocene seas were for the most part rather shallow and in the later Eocene particu- larly were bordered by wide tide flats and marshes. In the region of Lower Lake in Lake County, Cal., in the Mojave Desert immediately north of the Sierra Madre, and in the vicinity of San Diego, the early Eocene (Martinez) sea was present, but later receded and these particular areas are believed to have been dry land during the later Eocene. The Mojave Desert basin may have been covered with freshwater at this later period as lake deposits believed to be largely of Eocene age are known from the region contiguous to it. ‘This would be in accordance with the conditions prevailing in eastern Oregon? and Washington’ where great lakes existed during Eocene time immediately east of what is now the Cascade Range, 1 Tacoma Folio, p. 2. 2J. C. Merriam, Bull. Dept. Geol. Univ. of Cal., Vol. Il, No. 9, p. 286, 1go0r. 3G. O. Smith, Mount Stewart and Ellensburg Folios, Washington. 234 RALPH ARNOLD and possibly also east of the Sierra Nevada. Erosion tending toward a base-leveling of the Sierra Nevada and other elevated portions of the Pacific Coast must have proceeded rapidly during the Eocene as is evidenced by the great thicknesses of strata laid down during the period and by the fact that high relief was not present during the Oligocene except in rare instances, although the Oligocene in general was a period of uplift for much of the Pacific Coast province. OROGENIC MOVEMENTS AND VOLCANIC ACTIVITY IN THE EOCENE After the deposition of the early Eocene came a period of temporary elevation, erosion, and great volcanic activity in Washington, Oregon, and northern California. Extensive basaltic eruptions through long conduits and over the eroded rock surfaces took place in eastern Wash- ington and western Oregon, while in the region of the Olympic Moun- tains and eastern Oregon basalt flows and volcanic outbursts were also taking place. Eocene volcanic disturbances so pronounced in the north do not appear to have affected the Sierra Nevada nor the coastal region of California south of the Klamath Mountains. CLIMATE DURING THE EOCENE The faunas and floras of the Eocene indicate subtropical condi- tions for this period at least as far north as Puget Sound. The marine faunas of the Pacific Coast Eocene are closely allied to those of the Eocene of the southern states and the Eocene shells, Corbicula, for instance, as a rule belong to groups showing a predilection for warm waters. ‘This supports the evidence offered by the floras which are of a decidedly tropical aspect. Doctor Knowlton has the following to say in connection with the flora of the Puget formation, which may be regarded as typical of the Washington, Oregon, and California Eocene: The lower beds [the Eocene portion of the Puget formation], on account of the abundance of ferns, gigantic palms, figs, and a number of genera now found in the West Indies and tropical South America, may be supposed to have enjoyed a much warmer, possibly a subtropical, temperature, while the presence of sumacs, chestnuts, birches, and sycamore in the upper beds [Oligocene and lower Miocene] would seem to indicate an approach to the conditions prevailing at the present day.? « Tacoma Folio, p. 3. TERTIARY FAUNAS OF 17HE PACIFIC COAST 235 THE OLIGOCENE PERIOD THE OLIGOCENE A PERIOD OF ELEVATION The Oligocene on the Pacific Coast was primarily a period of eleva- tion and erosion over many areas which are now land. As indicated by the fine character of most of the sediment deposited during the period, the relief was not strong, except in a few regions. Outside the Washington - Oregon province there are few evidences of the period, except a more or less marked un- conformity between the Eocene and lower Miocene, and these for the most part are on the extreme con- tinental border or along the edges of the provinces of persistent sub- sidence. The extreme localization of the post-Eocene movements is well shown in the southwestern San Joaquin Valley where the lower Miocene and Eocene are apparently conformable and again occur within a distance of a quarter of a mile separated by a profound angular unconformity. Strata of undoubted a= Oligocene age consisting largely of Joveseoe | fred sandy to clayey shales and carrying Rarer Arnel i808 =| io a characteristic marine fauna are Fic. 2.—Map showing hypothetical found at many localities throughout distribution of land and water on the the Puget Sound and northwestern atic Coast during Oligocene time. Oregon areas and an isolated occurrence of similar beds is found in the Santa Cruz Mountains, a short distance south of San Francisco. Wherever their relations are known these beds lie conformable with the Eocene below and lower Miocene above; they therefore mark areas of persistent subsidence. A characteristic reddish to lavender formation (the Sespe), consisting of sandstone, shale, and some conglomerate found in Ventura and Los Angeles ———— ne SSS = — 236 RALPH ARNOLD counties in southern California, has been doubtfully referred to the Oligocene and the map made to agree with this correlation; but it is possible this formation is Eocene. Certain marine shales and sands underlying the lower Miocene beds in western Fresno and Kern County may also belong to the Oligocene. If so they imply that an arm of the sea remained in the San Joaquin Valley following the post-Eocene elevation that excluded marine conditions from much of the coastal belt of western America. The total thickness of the Oligocene over the region where it has been recognized varies from over 1,000 feet in Washington to 2,300+ feet in the Santa Cruz Mountains. The Sespe formation of Ventura and Santa Barbara counties, which has been tentatively correlated with the Oligocene, attains a maximum thickness of about 4,300 feet. CONDITIONS OF EROSION AND DEPOSITION With the close of the Arago stage (Eocene) the Klamath Moun- tains and Coast Ranges of Oregon and California were uplifted to a moderate elevation and subjected to extensive erosion, in some localities completely removing the sediments deposited during the Eocene. With the possible exception of an area in Ventura County in southern California no mountains of strong relief contributed directly to the Oligocene sediments. In eastern Washington the great lakes which prevailed during the Eocene were elevated and the sediments which had been deposited in them were folded and eroded, the resulting detritus in addition to large quantities of volcanic ejectamenta being collected in bodies of freshwater in eastern Oregon farther south. It is thus known that with the elevation of this northern country volcanic activity still continued although on an insignificant scale as compared with the periods preceding and following the Oligocene. In California there is no evidence of volcanism in the Oligocene period. FAUNA AND CLIMATE OF THE OLIGOCENE What little is definitely known concerning the faunas of the Oligocene as a whole indicates their closer affiliation to the Miocene than to the Eocene. The fauna from the Oligocene of the Santa Cruz Mountains (San Lorenzo formation) and a similar fauna from tJ. S. Diller, Roseburg Folio. TERTIARY FAUNAS OF THE PACIFIC COAST 237 Porter near Grays Harbor, in western Washington, are believed to be the oldest of the definitely known Oligocene. In these assemblages are several species showing distinct Eocene affinities; in the later Oligocene the forms are decidedly more closely allied to Miocene forms. The climatic conditions prevalent on the west coast of the United States during the Oligocene are believed to have been transi- tional from the subtropical of the Eocene to the more temperate of the lower Miocene. THE LOWER MIOCENE PERIOD CONDITIONS INAUGURATING THE LOWER MIOCENE The Oligocene period of elevation and moderate erosion was followed by diastrophic movements of a most interesting and important character. It was during this post-Oligocene period of disturbance that definitely recognizable movements along what is now termed the great earthquake rift and associated rifts of California first took place. Although profound regional subsidence was the rule in central and portions of southern California, local movements along the faults mentioned elevated: blocks of the pre-existing formations into islands, usually of considerable relief, in the region now occupied by the Coast Ranges. It is in a study of details such as the distribu- tion of the land and water in these fault zones that composite maps, such as those accompanying this paper, become entirely inadequate and sometimes misleading. Suffice to say that beginning with the pre-Vaqueros (pre-lower Miocene) period of disturbance many of the major blocks within the general fault zone of the Coast Ranges, and to a lesser extent, the minor blocks within the major masses, were seldom at rest for more than relatively short periods up to the present day. Some folding took place during the pre-Vaqueros period, but it was local in character, such as that exhibited in the Coalinga district, and of minor importance as compared with the vertical movements of the large masses. One of the most significant facts in connection with the lower Miocene subsidence was the retention of its position above sea-level of the Sacramento Valley region at a time when the San Joaquin Valley to the south was subjected to marine conditions. This discordance of movement between the two ends of a continuous basin, which in the discussion of California 238 RALPH ARNOLD geology has heretofore been considered as a unit, is believed to be related to the positive or upward-tending forces accompanying or immediately preceding the important volcanic activity which took place during early Miocene’ time adjacent to the Sacramento Valley, + ll HUTT ll ii ) NP | LAM a, “Ralph Arnold, 1904 Fic. 3.—Map showing hypothetical distribution of land and water on the Pacific Coast during lower Miocene time. sandstone. The Monterey, and northward into Washington, but which are absent or insignificant in the region contiguous to the San Joaquin. In this connection it is also worthy of note that the greater part of the Willamette Valley was also out of water during the lower Miocene.? DISTRIBUTION AND CHARACTER OF SEDIMENTS The Vaqueros or lower Miocene proper, and the Monterey or lower middle Miocene epochs have been included in mapping and discussing the lower Miocene, for together they mark by subsidence the beginning of a new geologic cycle following the Oligocene elevation. Locally the Vaqueros and Monterey have totally unlike histories. The Vaque- ros in the Coast Ranges of central California is characteristically con- glomeratic at the base, and sandy, with minor quantities of shale, in its upper portion. In the northern part of southern California it is largely dark arenaceous shale as- sociated with minor quantities of on the other hand, is composed largely of diatomaceous material with minor quantities of sand- stone, fine volcanic ejectamenta, and limestone, the last three 1 J. C. Merriam, Bull. Dept. Geol. Univ. Cal., Vol. V, p. 173. 2 Oral communication from Mr. Chester W. Washburne. TERTIARY FAUNAS OF THE PACIFIC COAST 239 usually more noticeable toward the base. The Modelo formation of Ventura County, the probable equivalent of the Monterey, con- tains two important coarse sandstone zones. In the region of Mount Diablo the Vaqueros and Monterey formations comprise alternations of sandstone and shale. In Washington and Oregon the whole lower Micoene is largely sandstone with some associated shale. A gradual gradation between the two formations is the rule, although their contact is often sharply marked and in some places is an angular unconformity.'' The thickness of the Vaqueros is as much as 3,000 feet, that of the Monterey over 5,000 feet, a total for the whole of the lower half of the Miocene of over 8,000 feet. CONDITIONS OF DEPOSITION The deposition of the lower Miocene (Vaqueros) sediments was inaugurated over much of the submerged territory, along the shores of islands of sharp relief. Erosion and deposition were rapid within local basins, especially in the region from the Santa Cruz Mountains southward to San Luis Obispo County, and still there were localities within these areas of intense sedimentation where deposition was slow. It is the belief of the writer that these variations were depend- ent, at least in part, on the positions of the areas in question relative to the steep or low slopes of tilted fault blocks. Over those portions of southern California, such for instance as in Ventura County, where the sea supposedly occupied the present land-area during the Oligocene, the conditions during the Vaqueros (lower Miocene) were quite different from those northward in the Coast Range archipelago. Instead of the littoral conditions accom- panied by rapid and coarse sedimentation of the latter province there was in the Ventura County area deep water with slower deposition and finer sediments, especially in the earlier Miocene. The lower middle Miocene (Monterey) shale formation is one of striking individuality, and conditions of unusual character prevailed during its period of deposition. The land which had begun to subside at the beginning of Miocene time, later, at the inauguration of the middle Miocene, sank over a large part of the region of Cali- « Branner, Newsom, and Arnold, Santa Cruz Folio. 2 For a fuller description of the Monterey see A. C. Lawson and J. D. L. C. Posada, Bull. Dept. Geol. Univ. Cal., Vol. I, pp. 22 ffi.; H. W. Fairbanks, zbid., Vol. II, pp. 9 ff.; Ralph Arnold and Robert Anderson, U. S. Geol. Survey Bull. 322, pp. 35 ff 240 RALPH ARNOLD fornia now occupied by the Coast Ranges and fairly deep water con- ditions became prevalent. A large area embraced between the Salinas and San Joaquin valleys and extending northward from the Antelope and Cholame valleys well toward the Livermore Valley was an exception to this general subsidence, and although much of it had been under water in Vaqueros time it was probably dry land or at least an area not subject to sedimentation during the Monterey. The wearing-away of extended land-areas ceased as they became sub- merged, and the material for the formation of coarse detrital deposits was no longer plentiful. Although the total thickness of the Monterey approximates a mile it is not probable that the depth of the sea at any time was as much as this, being more likely closer to half a mile. During the period of transition between the Vaqueros and the Monterey, limestone was formed chiefly, but somewhat inclosed basins where deposits of alkaline mud were laid down apparently existed in places. Such a basin is indicated by the alkaline gypsifer- ous clays on the south side of the Casmalia Hills, in northwestern Santa Barbara County, probably representing upper Vaqueros. During the early part of the middle Miocene (Monterey) time conditions were variable, calcareous and siliceous deposits alternating, probably as a result of alternating temporary predominance in the sea of organisms with calcareous or siliceous shells. As the period progressed the siliceous organisms became more predominant and remained so, making up a large fraction of the total bulk of the Monterey formation. It was anageof diatoms. ‘These small marine plants lived in extreme abundance in the sea and fell in showers with their siliceous tests to add to the accumulating ooze of the ocean bottom, just as they are forming ooze at the present day in some oceanic waters. It is well known that diatoms multiply with extreme rapidity. It has been calculated that, starting with a single individual, the offspring may number 1,000,000 within a month. One can con- ceive that under very favorable life conditions, such as must have existed, the diatom frustules may have accumulated rapidly at the sea bottom and aided the fine siliceous and argillaceous sediments in the quick building-up of the thick deposits of middle Miocene time, some of which are a mile through. ‘These diatomaceous shales are the source of some of the richest petroleum deposits of California. TERTIARY FAUNAS OF THE PACIFIC COAST 241 VOLCANIC ACTIVITY IN THE LOWER MIOCENE The most important display of volcanic phenomena on the Pacific Coast took place during the early and middle Miocene, and probably reached its climax at the time of the widespread post-early middle Miocene (post-Monterey) disturbances. Great volcanoes were active throughout eastern Washington and Oregon and in the Coast Ranges of California from the Santa Cruz Mountains at least as far south as the Santa Ana Mountains in Orange County. ‘The lavas and tuffs emitted by these volcanoes, and the associated intrusions, were basic in character. Certain facies of the Monterey are believed by Lawson and Posada‘ to consist of fine volcanic ash ejected from distant volcanoes of the period. FAUNAS AND CLIMATE OF THE LOWER MIOCENE The marine faunas of the lower Miocene or Vaqueros are well known and of widespread occurrence in the Coast Ranges of Cali- fornia; those of the Monterey, owing to the peculiar character of its sediments, are meager and little understood. A general survey of the fauna, however, indicates conditions approximate to those now existing in the coastal provinces, although certain forms of southern extraction, such as large cone shells, numerous arcas, and other types, indicate possible warmer environment. ‘The evidence of the mol- lusks is supported by that of the plant remains, at least in so far as it relates to the region of Puget Sound, for there, according to Knowlton,’ the presence of sumacs, chestnuts, birches, and sycamores in the upper Puget group [probable lower Miocene] would seem to indicate an approach from the subtropical conditions of the Eocene to the conditions prevailing at the present day. PERIOD OF DIASTROPHISM IN THE MIDDLE MIOCENE One of the most widespread and important periods of diastro- phism in the Tertiary history of the Pacific Coast was that immediately following the deposition of the Monterey or lower middle Miocene. Its effects are visible from Puget Sound to southern California. It is marked as much by readjustment, by local faulting and folding as by general movements of elevation and subsidence. In some regions the t Bull. Dept. Geol. Univ. Cal., Vol. 1, pp. 24 ff. 2 Tacoma Folto, p. 3. 242 RALPH ARNOLD folding and faulting were intense, the greatest disturbances accom- panying the uplift of the mountain ranges to an altitude of thousands of feet. In other regions low broad folds were formed during the post-Monterey disturbance, and the strata were not upheaved to a great altitude. Faulting on a most magnificent scale took place along the earthquake rift and certain other fault-zones, especially that in the Salinas Valley, and along these lines of displacement, masses of granitic rocks, which during the preceding epoch had been subject to little or no erosion, were suddenly thrust upward and left exposed to the ravages of streams that assumed the proportions of torrents in certain regions, as for instance adjacent to the Carrizo Plain in south- central California. The post-Monterey disatrophic movements in the Puget Sound province also produced sharp relief as is evidenced by the coarse sediments deposited immediately following the disturb- ance. The localization of movement during the period is exemplified at numerous localities in the Coast Ranges. Throughout much of the coastal belt, and probably likewise in the interior, great volcanic activity took place during the middle Miocene, this being the last epoch of volcanism in the Coast Ranges south of San Francisco. During this post-Monterey period of diastrophism general subsidence took place over most of the areas which were under water during the lower Miocene, and, in addition, extended northward from San Francisco Bay into the Sacramento Valley and along the coast to the California-Oregon line and south- ward down the Willamette Valley of Oregon. A new channel was ‘apparently opened across the northwestern end of the Olympic Peninsula, and the Colorado Desert country of southern California and Arizona which for a very long time had presumably been free from marine conditions was occupied by an arm of the sea. THE UPPER MIOCENE PERIOD DISTRIBUTION AND CONDITIONS OF DEPOSITION With the possible exception of that in the Eocene the subsidence immediately preceding and extending into the upper Miocene was the most important in the Tertiary history of the Pacific Coast. As a result, the formations of this epoch occupy a very considerable percentage of the surface of the present land-area. The sediments TERTIARY FAUNAS OF THE PACIFIC COAST 243 in the southern Coast Ranges, especially, are largely derived from granitic rocks and are usually coarser at the base, becoming finer and finer toward the top, possibly indi- ya" ar us" ar ra we cating a subsidence greater than the eee ica concomitant sedimentation. Excep- ES Mane Pie c “Gas bse, tions to the rule of coarse basal (1 rec snoeeren cas rt adlem = eke sediments are not uncommon, how- ever, and in the Santa Cruz Mountains and also in eastern |, E Monterey County, Cal., the uncon- ee ale. formable deposition of fine shale 4 : } directly upon older rocks is a well- | yp \ é - marked phenomenon. This, of = fe io course, indicated a sudden and } i rather deep submergence of the py iv 5 / areas in question at the initi ation ae eee ie of the upper Miocene. Conditions | : \ favoring the life of diatoms, so ES s marked in the Monterey, continued J = D | over part of the Monterey diato- 5 ‘ ar maceous shale territory during the 3 , upper Miocene (Santa Margarita | Sh | and Fernando formations). The SSS = = ji areas of maximum deposition | Upper Miocene iy -Es during the period were apparently Mayr Aeneda,naea on the southwestern side of the San Fic. 4.—Map showing hypothetical Joaquin Valley in western Fresno distribution of land and water on the County and in central Ventura pea Coase (dumiog upper Miocene County, Cal., where thicknesses of over 8,000 feet of sediments, belonging largely to the upper Miocene, occur. EROSION AND VOLCANIC ACTIVITY The peneplanation of the Klamath Mountains and the Sierra Nevada was probably completed during the upper Miocene, the detrital material from these land areas forming the great deposits in the San Joaquin and Sacramento valleys and the coastal belt of northern California. Erosion was practically continuous in these 244 RALPH ARNOLD first-mentioned areas from the beginning of the Eocene, but the final approach toward base level was probably not attained until the close of the upper Miocene. Volcanic activity had ceased on the Coast Ranges south of San Francisco during the inauguration of the upper Miocene, and had become subdued if not suppressed in the coastal belt to the north. In Oregon’ and possibly also in the vicinity of Mount Diablo, east of San Francisco, in northeastern California, and in Washington volcanoes still persisted. FAUNAS AND CLIMATE OF THE UPPER MIOCENE The upper Miocene as here mapped and described embraces several formations, each carrying a more or less well-defined fauna. The most characteristic of these, in the order of age, are the Santa Margarita, typically developed in San Luis Obispo and Monterey counties, Cal., the Empire of Oregon, and the San Pablo of the San Joaquin Valley. All three of these indicate conditions approaching those of the present day, though leaning toward warmer climates. Toward the end of the Miocene and the beginning of the Pliocene, the forerunners of the upper Pliocene sub-boreal invasion which was to come, began to be felt. A cool-water fauna is found in the upper- most Etchegoin (upper Miocene) formation in the Coalinga district, this being followed by a freshwater fauna. In the lower Pliocene faunas of southern California are the last representatives of certain unique species of Pecten which were abundant in the upper Miocene of central California, but which migrated southward during the late Miocene, and became extinct before the Pliocene in the territory where they formerly had been so abundant. The abundance of huge oysters, pectens, and certain subtropical echinoid types in the Santa Margarita implies shallow, rather warm, water—these con- ditions being due in part, at least, to the local sheltered bodies of water which occupied the southern Coast Ranges during that period. The Empire fauna, best developed along the edge of the open upper Miocene ocean, extended from at least as far north as the Straits of Fuca to the region of the Santa Cruz Mountains and possibly farther south. The strong resemblance between the Etchegoin fauna of the 1 J.C. Merriam, Bull. Dept. Geol. Univ. Cal., Vol. V, p. 173. TERTIARY FAUNAS OF THE PACIFIC COAST 245 Kettleman Hills in southern Fresno County, Cal., and the Carrizo Creek beds of the Gulf province of southeastern California has led to the correlation of the latter with the former, although the writer’s first examination of the Carrizo Creek fossils led to his placing them tentatively in the lower Miocene.* This correlation of the beds with the upper Miocene seems best to fit the conclusions based on other criteria such as faunal relations, character of sediments, sequence of geologic events in this province, etc. THE PLIOCENE AND QUATERNARY PERIODS CONDITIONS OF DEPOSITION AND CHARACTER OF SEDIMENTS Sedimentation was continuous from the Miocene through the Pliocene and on into the Quaternary over large areas along the Pacific Coast, but there was a marked change in the conditions sur- rounding the deposition at various times within this long period. In a limited coastal belt, marine conditions marked the Pliocene and Quaternary as well as the upper Miocene, while farther inland fresh- water, possibly alternating with short brackish-water or even marine, conditions prevailed during the Pliocene and Quarternary. This change from marine to lacustrine environment in the basin provinces of the Coast Ranges was probably brought about by two causes: first, a gradual elevation of the whole coast, and second, as suggested by Newsom,” movements along the earthquake rift and other faults in which certain of the blocks were elevated, forming barriers across pre-existing channels between the interior basins and the ocean. Faunal evidence indicates that those basins farthest inland, such as the San Joaquin Valley, became fresh possibly earlier in the Pliocene than those nearer the sea, such as the Santa Clara Valley basin. The marine Pliocene deposits consist largely of fine sand and soft shale, and sometimes marl, while the freshwater sediments usually include considerable thicknesses of coarse, more or less incoherent gravels, hardened silt and sands. ‘The maximum thickness of the marine Pliocene is attained in the Merced section immediately south of San Francisco, where approximately 4,000 feet of strata of Pliocene age are exposed. The greatest thickness of freshwater 1 Science, N. S., Vol. XIX, 1904, p. 503. 2 “Santa Cruz Folio,” Geologic Atlas U. S., 1909. 240 RALPH ARNOLD Pliocene occurs along the southwestern border of the San Joaquin Valley in western Fresno and Kings counties where the Tulare formation, largely of Pliocene age, attains a thickness of about 3,000 feet. DIASTROPHISM AND VOLCANISM IN THE PLIOCENE The most important movements inaugurating the Pliocene seem to have been an elevation of the Sacramento Valley and certain por- LEGEND E= MARINE A HU FRESHWATER = . TT ll ve i | | | Priocene E Rah Armotaaoa F Fic. 5.—Map showing hypothetical distribution of land and water on the Pacific Coast during Pliocene time. tions of the coastal belt of northern California and Oregon and _ the closing of the connection between the south end of the San Joaquin Valley and the southern California province. Although sedimentation was practically continuous from the Pliocene into the lowest part of the Pleistocene over much of the Pacific Coast, there is in parts of southern California a sharp line of uncon- formity between the Pliocene and Pleistocene. The extreme localiza- tion of the movements producing this unconformity is well exemplified at San Pedro, near Los Angeles, where the Pleistocene is separated from the Pliocene by an angular unconformity at Deadman Island, while half a mile distant on the mainland the same formations are perfectly conformable. Volcanic activities of a more or less com- plicated nature took place in certain portions of northern and central California during the Pliocene, while in the same period and probably up to a very recent date certain areas in the Sierra Nevada and Cascades have felt the effect of volcanism to a marked degree. TERTIARY FAUNAS OF THE PACIFIC COAST 247 DIASTROPHISM IN THE QUATERNARY Important and more or less widespread periods of diastrophism later than the one terminating the Monterey (middle Miocene) period of deposition occur in the Pleistocene. Up to the time of the discovery of certain indisputable evidence’ regarding the Pleistocene age of beds affected by certain of these latest mountain-forming movements, the diastrophism had been considered as closing the Pliocene and initiating the Pleistocene. Minor movements produ- cing local unconformities took place in central and southern Cali- fornia at various times during the Pleistocene in addition to the more far-reaching disturbances in the same epoch. ‘The latest diastrophism, including the elevations and subsidences of the coast line, the recent movements along the earthquake rift, etc., are familiar to all. The localization of many of these movements is known already; the locali- zation of many more of them will, it is believed, become clear when they are studied in detail. FAUNAS AND CLIMATE OF THE PLIOCENE AND PLEISTOCENE The faunas of the Pliocene and Pleistocene freshwater deposits are closely related and in some cases almost identical to the living faunas of the same province, while the marine faunas, on the other hand, indicate profound variation of environment, at least as regards temperature. Dr. Philip P. Carpenter? was the first to point out the cold-water faunas of the upper Pliocene and lower Pleistocene of the Pacific Coast. His conclusions have been strengthened by later workers, and in addition it has been shown that the latest Pleistocene faunas of the same region are of a type more tropical than those now inhabiting the shores of the Pacific Coast of the United States. It is thus evident that the warm temperature of the upper Miocene gave place to cooler conditions just before or at the beginning of the lower Pliocene, and to sub-boreal conditions in the upper Pliocene and lower Pleistocene. The later Pleistocene showed a very marked increase in oceanic temperature over the lower Pleistocene, even approaching subtropical warmth, and this, in turn, being followed by the conditions now prevailing. At some time during the upper 1 Mem. Cal. Acad. Sci., Vol. III, 1903, pp. 53-55. 2 Ann. and Mag. Nat. Hist., 3d Ser., Vol. XVII, 1866, p. 275. 248 RALPH ARNOLD Miocene and Pliocene, conditions prevailed favoring the migration of similar faunas into Japan and California or intermigration between the two. This is shown by the close similarity of certain pectens found in the upper Miocene in California, in still later beds in Alaska, and in the living fauna of Japan. The general resemblance of the late Tertiary faunas of California and Japan also favors this conclu- sion. SUMMARY AND CONCLUSIONS SUMMARY Following the period of elevation and erosion at the close of the Cretaceous, the Eocene was inaugurated by a subsidence below sea- level of the greater part of western Washington and Oregon and the western part of central and southern California. Volcanic activity was pronounced in the early and middle Eocene. Later in the Eocene brackish- and freshwater conditions prevailed over the same area, and extended over much of Alaska. The fauna and flora of the Eocene were tropical to subtropical. The Oligocene was a period of elevation with marine conditions restricted to a much smaller area than in the Eocene. The fauna was transitional with stronger affinities toward the Miocene. ‘The lower Miocene marked a wide- spread subsidence in the coastal belt which was followed by a period of mountain building and great local deformation, volcanism, etc. The Miocene faunas and floras indicate conditions comparable with those of the present day, or possibly a little warmer, except at the very close, when cool conditions began to prevail. The upper Miocene was a period of subsidence, with ideal conditions for maxi- mum deposition of sediments in local basins. During Pliocene and early Pleistocene time there was a continuation of many of the upper Miocene conditions, except that marine environment gave place locally to freshwater. The marine fauna of the upper Pliocene and lower Pleistocene indicates sub-boreal conditions in southern Cali- fornia, followed by conditions in the middle or later Pleistocene more tropical than those of today. A period of elevation and considerable local deformation in the early Pleistocene inaugurated the present conditions on the Pacific Coast. Many of the movements occurring throughout the Tertiary were of local extent, and, for that reason, TERTIARY FAUNAS OF THE PACIFIC COAST 249 correlation on a basis of diastrophism, unsupported by paleontologic evidence, is extremely hazardous. CYCLES OF DIASTROPHISM The period of the Tertiary uplift of the last worldwide cycle of diastrophism has been marked by two complete subcycles in the Pacific Coast of North America. The first was begun with gradual submergence in early Eocene, was continued by a gradual elevation in the later Eocene when marine conditions gave place to brackish- or freshwater conditions, and was completed by the epoch of uplift and erosion in the Oligocene. The second was initiated by submer- gence in the Miocene, was continued by the gradual elevation in the Pliocene, when, as in the later Eocene, freshwater conditions sup- planted marine, and has been practically completed by the Quaternary uplift which marks the present position of the continent. PERIODS OF MAXIMUM ELEVATION AND SUBSIDENCE The periods of marked elevation were the Oligocene, late Plio- cene, and Quaternary; the periods of maximum subsidence were the middle Eocene and upper Miocene; the periods of greatest volcanic activity were the middle Eocene and the middle Miocene. It is note- worthy that the periods of maximum volcanic activity were practically coincident with the periods of maximum subsidence in adjacent areas. CHANGES IN CLIMATE The climate was tropical to subtropical in the Eocene, transitional from this to warm temperate in the Oligocene, warm temperate in the Miocene, transitional from this to sub-boreal in the lower Pliocene, sub-boreal in the upper Pliocene and lower Pleistocene, and warm temperate in the later Pleistocene. DIASTROPHIC PROVINCES The study of the Tertiary history of the Pacific Coast shows the following positive elements or areas of persistent uplift in the coastal belt: The Olympic Mountains; a more or less uncertain, probably disconnected, belt along the western part of Washington and Oregon; the region of the California-Oregon line and thence eastward toward the Blue Mountains of southeastern Washington; the Santa Lucia Range, south of Monterey Bay; the region north and northeast of 250 RALPH ARNOLD San Diego; and the Peninsula of Lower California. The Sierra Nevada and Sierra Madre and San Bernardino and San Jacinto mountains may also be considered in the same class. The region of Santa Catalina and San Clemente islands off southern California belong to an area about which little is known previous to the Miocene, although it is the belief of the writer that they are in a belt of more or less persistent uplift. The negative elements or areas of persistent subsidence are: Puget Sound; the Willamette Valley; the San Joaquin Valley, and the Sacramento Valley to a less degree; central Ventura County; and, since the Eocene, the Salinas Valley, and the vicinity of Los Angeles. ioral |. Coalinga Ventura Los Angeles San Diego District County County Region Alluvium Alluvyium Alluvium Alluvium Stream Deposits —Unconformity— San Pedro San Pedro —Unconformity— —Unconformity— Beds at Deadman Is. 2 as =| i= Beds at Third St. Tunnel San Diego ° and Temescal ° g Canyon Z so] oS =| | u =] oO vo . Ry Ry —Unconformity— Beds at Etchegoin Carrizo Creek —Unconformity— Jacolitos Santa Margarita —Unconformity— —Unconformity— Modelo —Unconformity— Vaqueros Vaqueros 2 \ © —Unconformity— Ae Sespe Sespe (Oligocene ?) (Oligocene ?) Tejon Chico Topatopa Chico —Unconformity— Martinez or Tejon Ron» y i ee i ‘ i on. Et “Bees — Aiton | Alt | tava | tata Alta d ; | n Lie Tae J eee ieee Ras art inks ee en miro ee * a mete et by a ar Ei nS gta ed etl Bieta eS A nt lg et ee ne = CHAPTER XIII CORRELATION OF THE CENOZOIC THROUGH ITS MAMMALIAN LIFE HENRY FAIRFIELD OSBORN American Museum of Natural History, New York City The sea borders of the United States may be correlated with each other and with those of Eurasia in Cenozoic times through their invertebrate life, but for the vast interior of the American continent we must depend chiefly upon the mammals and in a less degree upon the reptiles, fishes, insects, and plants. I foresee great aid through these latter sources, but it is clear that the mammals will always afford the chief means of correlation, since in all parts of Europe mammal-bearing formations alternate with marine shell- bearing formations. The standard divisions of Cenozoic geologic time will always be those established in Europe. The problem set before the paleontolo- gists of our country is therefore to compare and establish our time divisions as closely as possible with the European standards. For this reason since 1899 I have been pursuing an exact investigation of the sequence of mammalian life in America and in the European Tertiary formations, and have enlisted the co-operation of many European and American paleontologists in the hope that such precise data may be obtained as to secure common understanding and usage of chronologic terms in the two countries. Previous to 1898 scattered attempts at the correlation of European horizons inter se were made by Dawkins, Schlosser, Osborn, Depéret, and others, but it was not until June, 1905, that there began in the Comptes rendus a remarkable series of papers by Depéret entitled “T/évolution des mammiferes tertiaires,’’ covering with fulness the whole subject of the succession of mammalian life in Europe, the correlation of all the known horizons, with theories as to the migra- tions between the continents of Eurasia, North America, and Africa. I am not in accord with Depéret on many of these theories but I 251 252 HENRY F. OSBORN accept in full his correlation of the mammal-bearing horizons on the continent, together with his subdivisions of geologic time. Similarly in America there are the pioneer correlations of Leidy of the American formations with each other and with those of Europe, followed with increasing precision by those of Cope, Marsh, Scott, Clarke, Dall,and Osborn. In 1899 Matthew published A Provisional Classification of the Freshwater Tertiary oj the West, and this together with his Faunal Lists of the Tertiary Mammalia oj the West, published in 1909, afforded the American bases for Osborn’s Cenozoic Mammal Horizons of Western North America, published in 1909, in which for the first time the succession of the mammalian life of the New and Old Worlds is closely compared. In the meantime increasingly accurate field methods, especially in the horizontal recording of levels after methods introduced by Osborn, Hatcher, and Wortman, have resulted in the subdivision of the old “formations” of Leidy, Cope, and Marsh into successive Lije- zones similar to those long in use in invertebrate paleontology. These life-zones are obviously as important in questions of time as they are in questions of phylogeny or descent; they narrow down the old correlation standard of the comparison of similar specific and generic stages to different levels; they add greatly to the possibilities of precise comparison in respect to the newer data of correlation, such as detailed evolution of related forms, the simultaneous introduction of new forms by migration, the predominance or abundance of certain forms, the convergence and divergence of American and European faunas. Putting together all these facts of various kinds, the first result is the proof that the mammalian life of Eurasia and America in Tertiary times passed through a series of grand phases of union, of divergence, of reunion, and perhaps again of divergence. There are seven of these phases. In the first, in Basal Eocene times, we find North America, Europe, and possibly South America peopled with archaic mammals of Mesozoic ancestry. In the second faunal phase, of Lower Eocene times, we observe the first modernization, which occurs simultaneously in Europe and North America, by the invasion of many modern families of mammals, CORRELATION OF THE CENOZOIC 253 which intermingled with the archaic; the life of Europe and North America continues to be very similar. In the third faunal phase, beginning in Middle Eocene times, the mammals of America and Europe gradually diverge and undergo an independent evolution with little or no faunal interchange; at the close of the Eocene the two faunas are very far apart. In the fourth faunal phase, beginning in Lower Oligocene times, there is a sudden reunion of New and Old World life. At the same time there occurs in both countries a second very surprising moderni- zation apparently by the further invasion of modern forms from the north. A jijth faunal phase occurs in the Middle Miocene, when there is a fresh reunion in the New and Old Worlds by the arrival in America of the proboscideans and the short-limbed rhinoceroses. Then follows a long period of independent evolution in the two countries until in the Middle Pliocene we enter a sixth faunal phase, in which a close land connection with South America is re-established, after an interval of separation reaching back into Eocene times. Finally a seventh faunal phase occurs in Pleistocene or Glacial times, when all the larger North American mammals become extinct, as well as the south American invading stocks, while North America is replenished by a large fauna from Eurasia. It will be noticed that these phases are in no way coincident either with the greater or with the lesser time divisions, for the obvious reason that these time divisions have all been established on the basis of the evolution of invertebrate life in Europe. EOCENE Basal.—The very opening of the Eocene furnishes one of the most brilliant examples of the possibilities of precise correlation through vertebrate life. Changes occurring in the interior of the American continent may be compared precisely with those along the northern coasts of France and Belgium. In each case great forms of reptilian life persist to the very close of the Cretaceous; the conditions of the American “Laramie,” ‘“‘Hell Creek,” or Ceratops beds are similar to those of the Danian or Maestrichtian of Belgium; both mark the abrupt termination of the Age of Reptiles; both are overlaid by beds HENRY F. OSBORN HORN(WASATCH DY Yoyyyy, GEG —Yy I yy isa o Fic. 1.—Map of southwestern Wyoming and northern Utah, showing partial areas of the Wasatch, Wind River, Bridger, and Uinta formations. Extensive areas A, B, lines of sections by F. B. Loomis. of the Wasatch are purposely omitted. CORRELATION OF THE CENOZOIC 255 containing a number of very distinctive types of archaic mammals mingled with those of distinctive reptiles (Champsosaurus) found alike in the Puerco of Mexico, the Fort Union of Montana, the F ; “WYOMING CONGLOMERATE” 200 E Ul 500 NONFOSSILIFEROUS Very barren SSS == eye eee == = Uintatherium D ; = (very abundant) 375 2 : : Mesatirhinus 5 eee Uintathertum Manteoceras OQ Fe LONE TREE. WHITE LAYER x a Cc , 350 Palaeosyops B (very abundant) 450° A 200’ Fic. 2.—Columnar section of the Bridger formation, Henrys Fork, western,Wyo- ming. After studies by Matthew and Granger, 1902. Thanetian of northern France. Thus we believe the opening of the Tertiary admits of close correlation in the Old and New Worlds. The succeeding rich Puerco-Torrejon mammalian life of New Mexico, so far as known, parallels that of the Thanetian (including the 256 HENRY F. OSBORN Cernaysian) stage of northwestern Europe. It is all Paleocene, or Basal Eocene. Lower.—The beginning of the Lower Eocene is clearly defined in the Rocky Mountain region and with equal sharpness in northern France and Belgium by the appearance of Coryphodon, and by the Diplacodon zone E==—— A\< Diplacodon << Artiodactyla and chief collection Be of Uinta mammals(smal!) sees Dsl aoa CORES chief fossi/iferous leve/ Amynodon zone Metarhinus LATER EOCENE OF UINTA BASIN Fic. 3.—Columnar section of the Uinta formation, northern Utah. In A and B the diagram does not properly represent the irregular nature of the so-called sand- stones and clays, which are probably in part coarser and finer volcanic-dust deposits. Modified from notes by O. A. Peterson, 1894. Faunistic studies by Osborn. opening of the second faunal phase with its advent of modernized life. Our Lower and Upper Wasatch correspond respectively with the Sparnacian and Ypresian stages of France. It is represented in deep and fairly rich exposures in northern New Mexico and in western, central, and northern Wyoming. CORRELATION OF THE CENOZOIC 257 The Wind River of central Wyoming together with the Lower Huerfano near the Spanish Peaks of Colorado marks the upper life- zone of Coryphodon and may prove to correspond closely with the Ypresian of France. In the Rocky Mountains the Wind River is read- ily distinguished by the survival of a number of characteristic Lower Eocene types (Coryphodon, Phenacodus) and the fresh arrival of a number of equally characteristic Middle Eocene types (uintatheres, titanotheres). It is consequently an ideal transition fauna. Unfor- tunately the formations believed to be of corresponding age in France are poor in mammal remains. From this time on to the summit of the Eocene we are passing into the third faunal phase, or divergence and independent evolution of the life of Europe and America. Consequently close correlation is almost impossible; at no period in the Tertiary were the Nearctic and Palearctic faunas so widely separated. Middle.—With the American Bridger, 1,800 feet in thickness, we enter the Middle Eocene and broadly compare the Lower Bridger with the Lutetian and the Upper Bridger with the Bartonian of France. The precise survey of the life-zones of the Bridger by Granger and Matthew marks one of the greatest advances of recent times. Similarly under the direction of the present writer the Washakie of central Wyoming has been surveyed precisely by Granger, proving that the Lower Washakie is identical in age and in its mammalian life with the Upper Bridger and broadly corresponds with the Barto- nian, or closing stage of the Middle Eocene of France. We are now in the Uintatherium Zone, all the famous discoveries of Cope and Marsh having been made at this level. Here belongs also the beginning of the Uinta deposition of northern Utah. We now pass into the Eobasileus Zone of the Upper Washakie and the Middle Uinta, in which the long-headed uintatheres described by Cope as Hobasileus and Loxolophodon occur mingled with remains of highly specialized Eocene titanotheres. This is apparently the lower level of the Upper Eocene and is broadly comparable with the Ludian stage of France. U pper.—The succeeding Ligurian stage of France may be paral- leled with the upper, or true Uinta, the Diplacodon Zone of Marsh. 258 HENRY F. OSBORN The zonal type is a large titanothere with well-developed bony horns, transitional in many characters to the Lower Oligocene titanotheres; in fact, the summit of the thick Diplacodon Zone of 600 feet will prob- ably prove to coincide with the base of the White River Group on the great plains. Quite recently, during the summer of 1909, the much- desired sequence of Oligocence and Eocene strata was discovered by Mr. Granger of the American Museum expedition. ‘The Diplacodon Zone has been discovered in the Wind River region of Wyoming underlying the Titanotherium Zone. The Ligurian stage of France is that of the famous Gypse de Montmartre discovered by Cuvier, full of paleotheres and anoplo- theres, a mammal fauna totally distinct from that of the Rocky Mountain region. OLIGOCENE Lower.—The Oligocene opens in the New and Old Worlds with the fourth faunal phase and second modernization, which since it affects alike Europe and America probably indicates a fresh migration from the great unknown northern, or Holarctic region. With this migration close faunal resemblance is re-established with western Europe, and thereby comes a welcome means of geologic correlation; in other words, we may with considerable confidence consider that the base of the White River group was nearly coincident with the inferior Tongrian of France. Sixteen new families of mammals appear in America, all of them still existing, and seventeen modern, or still existing, families appear in Europe. This momentous faunal change in North America is partly attributable to the fact that this is our first glimpse of the life of the Great Plains. Middle-—The Lower Oligocene, or Titanotherium Zone, most accurately surveyed by Hatcher, is succeeded by the Middle Oligocene or Oreodon Zone, broadly comparable with the Superior Tongrian and Stampian of France, both containing similar types of amphibious rhinoceroses and many other mammals. One of the chief points of interest here is the sharp separation discovered by Matthew between the plains-living mammals buried in the so-called clays, or finer deposits, and the forest-living mammals buried in the coarser intrusive river sandstones. ‘Lo6r ‘uiogsQ “ET puke MONI “G “M qayyy ‘[euoueauod Ajaind are fay} ‘ayeos 0} poyuasaidar Jou a1 suOT}DeS esau} ‘sain8y J0Y}0 dy} UI SUOTJOAS By} OYTJU “pepslose1 used 2AvY s[eUIUeUT [ISSOJ YOTYM UT JSaA\ OY} Jo SuONeUTIOF pue spsodap oUad0}sI9[q-2U290311O jeyuoutuostda Joryd ay} Jo ouIOS Jo uOTRJaLI09 [eUOISIACIG—P “Ol NOOSTHO VNV.LNOW VLOMVU'S GNV VHSVYEAIN [oi See ee ———— TDL. 0UD?22 = —————— Sn ae ou ———S ee ——<————ees =—NowdvHo——J ee i SSS mee eens =F rs a SS ——— uopoukumayy | ———————— ——————— SS eel Oa et PUD UOpoIlQ —_—_—— eae {_——— 3N3909110 ‘LNOW ‘SWHOdAaauHL MNVDOT LHOT Y 4 = = : a7100IW wee we ~ eS ee oe ee yYaMo? B10G0IW 3N390NMd BN3IDOLSI3Id O = V ¥, \ ad =) y . r. ~ rag NOpauO = 0S = *4 NOZINOH ‘— Regs VASVUdAN TVHINGO snnbyz = 3NOZ S 200 HENRY F. OSBORN U pper.—The close of the Oligocene takes us into the John Day tuff deposits of Oregon, and is generally parallel with the Aquitanian Stage of France, typified by St. Gérand-le-Puy. It is the Dicera- therium Zone, or the climax of the evolution of the pair-horned rhinoceroses in both countries. We pass also into the Upper Mery- cochoerus Zone at the summit of the John Day and at the base of the Arikaree formation extending along Pine Ridge of South Dakota. Here we are again in difficulty in determining just when the American Oligocene should be regarded as closing and the Miocene as beginning. An abundance of diceratheres and entelodonts still betokens Oligocene times, but it is possible that we may be in the Miocene. This is one of the doubtful points requiring further investigation. MIOCENE The solution of the Lower and Middle Miocene sequence in America through the discoveries of Hatcher, Peterson, and of Matthew marks another great advance of recent years. Lower.—There is no question that in the Upper Arikaree, the Upper Harrison of Hatcher, and the Upper Rosebud of Matthew we are fairly in Lower Miocene times corresponding with the Burdigalian of Europe. There is now considerable faunal difference between the New and Old Worlds. The Proboscidea certainly enter Europe at this time, and one of the debated points is when they first appear in North America. Middle.-—The Vindobonian, or Middle Miocene of Europe, divided into the three successive stages of Sansan, Simorre, and St. Gaudens, is again with considerable confidence compared with the Deep River of Montana, and the Pawnee Buttes of Colorado, through the researches of Scott and Matthew. Here we enter the fifth faunal phase, marked by fresh migrations and the first undoubted appear- ance of the proboscideans and short-limbed rhinoceroses in America, both arrivals from the Old World. Physiographic changes are indicated in evidence of increasing summer droughts, numerical increase of animals adapted to plains-living and the semi-arid con- ditions, in the disappearance of most of the browsing types. The correlation is, however, by no means close at present, because the life of Europe and the great American plains is of different local habitat. CORRELATION OF THE CENOZOIC 201 U pper.—In the Upper Miocene, however, we are again somewhat more confident in correlating our Hipparion and Procamelus Zone, the “Loup Fork” of early writers, with the Pontian or Pikermi stage of Europe typified by the wonderful advent of the plains fauna of Asia which spreads all over southern Europe, probably into Africa and the far East of southern Asia and China. PLIOCENE It is difficult again to demarkate the close of our Miocene and the beginning of our Pliocene. For the first time in American Tertiary history an invertebrate paleontologist (Dall) comes to our aid through discovering that the mammals of the Alachua Clays of Florida overlie certain true Lower Pliocene molluscs. The mammals of these clays are comparable to those of the Republican River of Kansas, and we are consequently disposed to place the latter in the Lower Pliocene. It is at least a more recent phase than the ‘“‘Loup Fork,” and is hence distinguished as the Peraceras Zone, from the presence of a number of broad-skulled hornless rhinoceroses. Lower.—Of undoubted Lower Pliocene age is the recently dis- covered Snake River deposit of western Nebraska, the Neotragocerus Zone, and the Virgin Valley and Thousand Creek of Nevada. The arrival at this time of true Old World tragocerine and hippotragine antelopes from Asia, as identified by Matthew and Merriam, is one of the most noteworthy discoveries in recent paleontology. These antelopes may prove to demarkate our Lower Pliocene, in which case the Republican River will be pushed back into the close of th Miocene because it certainly does not contain these Old World forms. The Lower Pliocene, or Plaisancian, of Europe is represented by the mammalian life of Casino, which is very sharply demarkated from that of Pikermi. Middle.—The Astian, or Middle Pliocene, life of France, typitied at Roussillon and Montpellier, is broadly comparable with the Blanco of Texas, where we enter the sixth faunal phase, marked by the inya- sion of South American armored edentates, or glyptodonts, into the southern United States. These deposits are accordingly known as the Glyptotherium Zone. They mark a great advance upon those of the Republican River. 262 HENRY F. OSBORN PRELIMINARY CORRELATION EUROPE ASIA NORTH AMERICA Upper SICILIAN Siwaliks “Loup River” Middle AsTIAN Siwaliks Blanco PLIOCENE Thousand Creek Lower PLAISANCIAN Siwaliks Rattlesnake and Republican River ( “Loup Fork” Upper PONTIAN Manchhar Madison Valley l Clarendon Deep River MIOCENE Middle VINDOBONIAN Manchhar Pawnee Buttes Mascall ( Arikaree Lower BURDIGALIAN “Upper Harrison” ( Rosebud AFRICA Harrison (Lower) Upper AQUITANIAN John Day | White River( Upper) te Ri : OLIGOCENE (Middle Srampran eens (uted) White River (Base) Lower SANNOISIAN Fayim ee ee | Chadron Uinta (Upper and Upper LUDIAN Faytim Middle) Washakie (Upper) Uinta (Lower) Middle BARTONIAN Washakie (Lower) Bridger (Upper) 5 Bridger (Lower) SS Huerfano (Upper) Bridger (Lower) UppER YPRESIAN Huerfano (Upper) EOCENE Green River Huerfano (Lower) Lower LOWER YPRESIAN Wind River Wasatch (Upper) SPARNACIAN (Upper Lande- Wasatch (Lower) nian of Belgium) UppEeR THANETIAN ( =Cernaysian) Torrejon (Lower Lande- Fort Union nian of Belgium) Basal LOWER THANETIAN | Be Sas CRETACEOUS Upper- DantAN=Maestrichtian FielGrecke most (Terrestrial) (Marine) CORRELATION OF THE CENOZOIC 263 U pper.—The Upper Pliocene, or Sicilian, stage of Europe, typified by the Val d’Arno fauna of northern Italy, is hardly comparable with any American horizon. We are here on the border-line between Pliocene and Pleistocene, and a great deal of research is still needed. The Peace Creek deposits of Florida (Dall) may help us because here we discover an Equus and an Elephas Zone overlaid by marine Upper Pliocene molluscs. Rather primitive forms of Equus and Elephas are also characteristic new arrivals of the Upper Pliocene, or Sicilian, stage of Europe. The same doubt applies to the little- known “Loup River” of Nebraska, in which Equus and Elephas were discovered by Leidy many years ago. PLEISTOCENE Perhaps the most striking determinations which await the mam- malian paleontologist are those which close comparison of the Pleisto- cene stages in the New and Old Worlds will afford. In Europe we have four great series of correlation data, namely: The geologic succession of the glacial depositions; The faunal succession especially among the higher mammals; The evolution of stone implements of human manufacture; Stages in the skeletal evolution of man. In America the two kinds of data connected with the evolution of man are entirely wanting, and we are thrown back on the geologic and the faunistic divisions; consequently close comparison in these two lines of evidence common to both countries is all the more neces- sary. In Europe it is possible to distinguish four grand faunistic phases, namely: The first early Pleistocene fauna, Eolithic Stage of culture; Second or mid-Pleistocene fauna, Eolithic and early Paleolithic Stages; Third or Upper Pleistocene fauna, late Paleolithic Stage; Fourth, post-Glacial fauna, Neolithic Stage. From close study of the Pleistocene life of North America there is promise of correlation with Europe through identification of American with European glacial and interglacial periods, through the discovery and identification of interglacial faunas, as in the Aftonian and Toronto deposits, through the careful recording of the time of extinc- 204 HENRY F. OSBORN tion of native types and of the time of arrival of new types to demarkate our Pleistocene also into great successive life-zones. The chief progress made thus far (1909) is that we begin to recog- nize the following divisions of American life: Early and mid-Pleistocene life of the plains, Equus Zone; Mid-Pleistocene life of the forested regions, Megalonyx Zone; Life of the maximum cold period, Ovibos Zone; Life of post-Glacial times, Zones of Cervus and Homo. Especially interesting is the coincidence of the maximum cold period, or Ovibos, Musk Sheep, Zone of America, with the maxi- mum cold period, or Elephas primigenius, Rangijfer tarandus Zone of Europe. It is obvious that we should never expect to discover as clear demarkation of the life-zones in America as in Europe because of the vast refuge areas of the mammals in the south. In Europe the glacial advances are sharply punctuated by the appearance and disappearance of species. In America apparently such appearances and disappearances are gradual. PRINCIPAL REFERENCES DEPERET, CHARLES, “L’évolution des mammiféres tertiaires,”’ Compt. Rend. Acad. Sct., Paris, June 5, July 3, November 6, 1905, March 12, 1906. Osporn, H. F., “Correlation between Tertiary Mammal Horizons of Europe and America; an Introduction to the More Exact Investigation of Tertiary Zodgeography; Preliminary Study, with Third Trial Sheet,” New York Acad. Sci. Ann., Vol. XIII (1900), pp. 1-64. ——., “Cenozoic Mammal Horizons of Western North America,” U. S. Geol. Surv. Bull. 361 (1909), pp. 1-138. Marttuew, W. D., “fA Provisional Classification of the Freshwater Tertiary of the West,” Am. Mus. Nat. Hist. Bull., Vol. XII (1899), pp. 19-77. , “‘Faunal Lists of the Tertiary Mammalia of the West,’ Appendix to ““Osborn’s Cenozoic Mammal Horizons of Western North America,” U. S Geol. Surv. Bull. 361, pp. 91-138. DAL, W. H., “A Table of the North American Tertiary Horizons Correlated with One Another and with Those of Western Europe: with Annotations,” U.S. Geol. Surv., r8th Ann. Rept. (1896-97), Part II, 1898. , ‘Age of the Peace Creek Bone Beds of Florida,” Acad. Nat. Sci. Phila. Proc. (1891) ,-p: 20. CHAPTER XIV PHYSICAL, GEOGRAPHY OF THE PLEISTOCENE WITH REFERENCE TO THE CORRELATION OF PLEISTOCENE FORMATIONS ROLLIN D. SALISBURY The University of Chicago The character of the changes which marked the transition from the Tertiary to the Quaternary were somewhat unusual, though not unique as they were once believed to be. Great as these changes were, they were probably not equal in magnitude or importance to the changes which marked the transition from one great era of the earth’s history to another. The significant changes at the close of the Tertiary are those which had to do (1) with the height and extent of the land and, perhaps as a result of these changes, (2) with pro- found alterations of climate, bringing on (3) glaciation on an extensive scale, and causing (4) migrations and mutations of life. I. THE PHYSIOGRAPHIC CHANGES The changes in altitude which affected the North American con- tinent late in the Tertiary have not, in most places, been worked out in such detail as to lead to numerical results in which implicit con- fidence can be placed; but the general tenor of the evidence is har- monious, and the main conclusions are probably correct in their general terms. ‘They may be summarized briefly as follows: 1. In the eastern part of the continent, the land is generally thought to have stood higher than before by some few hundred feet. If the more extreme views of a few of the geologists who have studied this question are accepted, the excess of elevation over the present was a few thousand feet. 2. In the larger part of the Mississippi basin, the gain in altitude was considerable, though still on a relatively moderate scale. In the eastern and central parts of the basin it is probably to be measured by a few hundreds of feet, rather than by figures of a larger denomina- 205 206 ROLLIN D. SALISBURY tion. ‘There is some reason for thinking that the important topo- graphic features of the central Mississippi basin are chiefly of late Tertiary and post-Tertiary origin, developed from a late Tertiary peneplain now represented by the summits of the higher hills and uplands of the region, a few hundred feet above the general level in which the present valleys are sunk. It is true that these summits have sometimes been interpreted as remnants of a Cretaceous pene- plain; but this conclusion is not firmly established, and the alternative suggested above is entitled to consideration. 3. In the west, the relative uplift in the closing stages of the Tertiary and early Pleistocene was greater. The estimates of the late Tertiary and post-Tertiary uplift here at one point and another range from several hundred feet to several thousand feet. The fig- ures are most definite and perhaps most satisfactory near the Pacific coast. In southern California, the uplift at this time has been estimated at 1,500 feet; in northern California, 1,500 to 2,000 feet; and in the Sierras at 3,000 to 6,000 feet. In Oregon, Pleistocene marine fossils are found up to elevations of 1,500 feet, while in and about the Cascade Mountains of Washington, an elevation of several thousand feet, maximum, seems to be well established. In British Columbia, the relative upwarp of the corresponding time has been thought to reach an amount comparable to that of the Cascade Range, while, farther north, most of the estimates point to less extensive changes. The old peneplain which is now at an eleva- tion of 6,000 to 9,000 feet in Washington and British Columbia, is thought to descend to 4,000 or 5,000 feet farther north. While the age of the deformation which brought the former peneplain of these northern lands to its present position has not been fixed with precision, the best opinion seems to place it, or at least its initiation, in the late Pliocene and early Pleistocene. Students of the western interior have reached no general agree- ment as to the amount of late Tertiary and Quaternary change of level, but there is general agreement that the land of that region was notably higher at the close of the Tertiary, and later, than it had been before. The increase in the height of the land amounted, perhaps, to a few thousand feet in some places, but was probably far from uniform. PHYSICAL GEOGRAPHY OF THE PLEISTOCENE 207 4. In the West Indies and Central America, the interpretation of facts and supposed facts seems to be more or less uncertain. Spencer would make the amount of change of level in the West Indies within this general period very great, even 8,000 to 11,000 feet higher than now. Hill would have some portions of Cuba at least 2,000 feet higher than now at or since the close of the Tertiary, and the Barbadoes 1,100 feet higher at about the same time, while Hershey thinks the Isthmus of Panama has been bowed up 1,000 feet or so since the beginning of the Pleistocene. If even the more moderate of these figures are correct, it appears that the average relative increase in the altitude of the continent must have amounted to several hundred feet at least. This amount of elevation must have been adequate (1) to increase erosion by streams greatly, this increase resulting both from (a) increase in precipitation, and (0) increase in gradient of the streams; (2) to lower in some slight measure at least the average temperature of the land, and to increase its range; and (3) to reduce the amount of vegetation on the average, both because of (a) the unfavorable change in temperature and (0) the more rapid erosion. Outside of North America, similar changes seem to have been in progress. ‘Thus in South America, such determinations as are at hand point to an elevation approaching 3,000 feet at a maximum on the west coast of South America, since the late Tertiary. Changes of similar import, and perhaps of comparable extent, are indicated by the facts reported from other continents, though for all but Europe, the facts are meager. In Europe, changes of level at the close of the Tertiary were not everywhere great, but about the borders of the Alps, the increase of elevation is estimated by Penck and Briickner to have been 300 to 500 meters. It should be noted that the deformations of this time were more important in affecting the height of the land than in affecting its area. Yet from the evidence of existing floras and faunas, it seems probable that the up-swelling of the contiguous parts of America and Asia were sufficient to connect them by way of the Aleutian Islands. Shaler and Spencer have urged reasons for thinking that Florida and Cuba were connected in the late Pliocene or early Pleistocene, but this con- clusion cannot be said to be established. In Europe, within the same 268 ROLLIN DPD. SALISBURY general period of time, England has probably been joined to the con- tinent, and southern Europe to Africa. Submerged valleys on the northwestern coast of Europe, if interpreted in the usual way, indicate elevations several hundred to a few thousand feet greater than those of the present, enough, if some of the estimates are correct, to have connected Europe with Greenland and North America. If such a connection existed, it must have entailed changes in oceanic circula- tion sufficient to have affected the climates of high latitudes in an important way. The very considerable changes at the beginning of the Quaternary were followed by a great succession of changes as the period pro- gressed. Some of them reinforced the changes just sketched, and some of them were of the opposite phase. Oscillations of level during the Quaternary have been more carefully worked out along the coast of northern Europe than in America. Unexpectedly enough, evidence seems to point to greater depression during the glacial epochs than during the interglacial. The amount of the determined oscilla- tions of level during the Quaternary range from a few feet to a few hundred feet. II. EFFECTS OF PHYSIOGRAPHIC CHANGES ON CLIMATE In many parts of the earth, as in the interior and eastern part of North America, in Europe, and elsewhere, the increase of elevation at the end of the Tertiary was probably not sufficient to be of great importance climatically, in a direct way. In other regions, as in the western part of North America, on the other hand, the gain in height was probably sufficient to produce considerable effects directly. In an indirect way, the effect of the increase of average altitude of land on climate may have been much more considerable. Erosion was stimulated by the increase of altitude and by the decrease of vegetation due to the causes already mentioned. ‘The increased rate of erosion led to the removal of the residual earths and alluvium which may well have accumulated on the surface to very considerable thickness, and the removal of these materials from the surface exposed the underlying rock to decay. If changes in the constitution of the atmosphere are to be regarded as the cause, or as even one cause of climatic change, the increase of PHYSICAL GEOGRAPHY OF THE PLEISTOCENE 209 erosion at the close of the Tertiary would have led to an increased consumption of carbon dioxide, and so may have been responsible for the initial step in the series of changes which brought on the glacial climate. Though it is, perhaps, too early to affirm that the increased altitude of the land at this time was the basal cause which led to the cold climate which followed, this is a hypothesis toward which students of glacial geology are looking with much hope. If the increased height of the land led to increased erosion, and so to increased consumption of carbon dioxide, the reduction of the amount of this gas in the atmosphere would have lowered the tempera- ture everywhere. The resulting decrease in the temperature of the sea would have led to an increased solution of carbon dioxide from the atmosphere, thus depleting the atmospheric supply still further, and this, in turn, reacted upon the temperature and became a cause of its further reduction. This cause, therefore, once in operation, must have continued with increased effectiveness until the decay of rock was checked by decrease of altitude or temperature, or by the accumulation of ice-sheets which protected the rock beneath from ready carbonation. Til. THE DIRECT IMPORTANCE OF THE ICE-SHEETS THEMSELVES Irrespective of the cause of the glacial climate, the covering of six million or more square miles of land in the northern hemisphere with ice hundreds and thousands of feet in thickness was in itself an extra- ordinary event which might well serve as an important landmark in geologic history. The ice-sheets, and especially the remarkable successions of ice-sheets, might appropriately be emphasized as proof of one of the most remarkable climatic incidents in the history of the earth, so faras now known. But apart from its great climatic signifi- cance, each ice-sheet meant the relatively rapid superposition upon the northern continents, over the great areas indicated, of a new layer of rock, the ice, which for tracts of millions of square miles must have had a thickness exceeding a thousand feet, and perhaps a thickness of several thousand feet. The aggregate volume of this new rock, superposed on the northern parts of the northern continents, was such that it could only have been measured in terms of millions of cubic miles. The withdrawal of its substance from the sea effected a cor- 270 ROLLIN D. SALISBURY responding lowering of its surface, an appropriate extension of land, and an increase in its height above the sea. Though this great body of rock new-laid upon the lands was temporary in its character, primarily because of the low temperature at which its substance assumed the liquid form, it was of great importance, from a geologic point of view, in more ways than one. 1. In the first place, the loading of millions of square miles of land with such a weight must have had an appreciable effect upon crustal movements, if the doctrine of isostasy has validity, and its disappear- ance, under climatic conditions which developed later, must have produced movements of the same class, but of opposite phase. 2. Again, the development of the ice-sheets put a virtual stop to the processes which had been in operation over six millions of square miles of the land, and set other processes into operation in the same places. ‘Thus the normal phases of river work were suspended, most rivers within the ice-covered area ceasing to flow altogether. The usual phases of rock weathering and decay were practically stopped over the same areas, areas which, in the aggregate, were a very con- siderable fraction of the surface of the land. On the other hand, a new process of erosion was substituted for the old—erosion not restricted chiefly to the removal of decayed rock. 3. The changes in erosion were hardly greater than those in sedimentation, for instead of the assortment and separation of decayed material into its several physical classes before deposition, fine sediments and coarse, largely of undecayed material, were left promiscuously commingled. ‘Thus on a large scale and over enor- mous areas deposits were made which were unlike those of comparable extent at any other stage of the earth’s history, unless at times when climates were similar. 4. It should be noted further that the changes in the processes of erosion and sedimentation—changes in kind as well as in rate—were not limited to the areas actually covered by the ice, or even to the areas affected by drainage from it, or by icebergs which floated out beyond its edge. Modifications of erosion and sedimentation were felt in all areas affected, directly or indirectly, by the change of climate. The great ice-sheets, with the recurrent disturbance which they probably occasioned in the crust of the earth and the lesser changes PHYSICAL GEOGRAPHY OF THE PLEISTOCENE 270. in the surface of the ocean; with their recurrent inhibition of the usual processes of erosion and sedimentation over great areas; with their recurrent modification of these processes over other great areas beyond the ice-sheets themselves; and with their recurrent inaugura- tion on a large scale of processes of erosion and sedimentation which were unusual, might, without consideration of further changes of an indirect character, furnish adequate bases for important time divisions. Especially is this the case since the influence of the ice-sheets must have been felt in a physical way, throughout most if not all the earth. IV. CHANGES IN LIFE The great changes in the physical processes which this on-com- ing of the ice-sheets brought into operation, effected corresponding changes in life and in the processes which depend on life. In the first place, the total amount of land life must have been greatly reduced. If account be taken of mountain glaciation in both hemi- spheres as well as of the ice-sheets, it is probably within the limits of truth to say that conditions became so far inhospitable as nearly to eliminate land life from about one-seventh of the land of the globe, and to have rendered conditions relatively inhospitable over a still larger area. The effect upon the life of the sea is less easily stated, but it also must have been great, for the average reduction of the tempera- ture of the sea must have been considerable. The crowding of land life off 8,000,000 square miles, more or less, must have tended to concentrate it upon the land which still remained hospitable, and to decimate or exterminate those forms which could not migrate readily. Migration must have been forced upon the sea life as well as upon that of the land, and the shifting of the zones of both must have resulted in a shifting of the sites of organic deposi- tion, perhaps especially of the sites where limestone was made. At the same time, the rate at which it was formed, the whole earth considered, was probably much reduced. It would seem, from the series of physical changes sketched, that very profound changes in life should have followed, but it must be confessed that, in spite of the conditions which it would seem must have been favorable for great destruction of life, and for imposing great modifications upon that which survived, statistical evidences of 272 ROLLIN D. SALISBURY the changes which followed are less impressive than would have been expected. The data at hand do point to extensive migrations, but not to the exterminations and profound modifications which might have been anticipated. It seems impossible to think that the changes of climate which drove musk oxen to Kentucky and Virginia, and Arctic plants and reindeer to the lowlands of central Europe and to the Mediterranean, were without very profound biologic significance, unless the life of the earth had reached a condition of far greater stability than that of earlier times, when lesser physical changes seem to have produced greater biological changes. One of the features of the late Tertiary land life, and especially of the floras, seems to have been the great extent to which types were mingled. This mingling of tropical or sub-tropical forms with temperate and boreal ones seems to have begun as early as the middle of the period. ‘The oscillations of climate which marked the Pleisto- cene seem to have had a sifting influence upon the migratory forms, and to have forced them to special adaptations and habitats as the period progressed. ‘This is suggested, for example, by the floras of America and Eurasia. Gray pointed out long ago that the forest flora of the eastern part of North America is more like that of Japan than like that of the western part of our own continent. In Europe, the north-south and south-north migration of the floras as ice-sheets advanced and receded was interfered with by the east-west mountain ranges and by the seas bordering Europe on the south. In eastern Asia and America, on the other hand, the back-and-forth migration of the floras was facilitated by the greater continuity of land between high and low latitudes, and in America at least, by the absence of east-west mountain ranges. In the western part of the United States, the irregular topography made repeated latitudinal migrations of the floras more difficult than in the eastern part, though perhaps less difficult than in Europe. In eastern Asia and in eastern America, where migration was relatively easy, the forest flora is much larger than in Europe or western North America. Thus Atlantic America and Pacific Asia have each 66 genera of forest trees, while Pacific America and Europe have but 31 and 33 genera respectively, and the number of species is approximately in keeping with the number of genera. PHVSICAL GEOGRAPHY OF THE PLEISTOCENE 273 Vulcanism has been regarded as a factor which decreased the flora in the western part of North America as compared with the eastern; but since the floras were much the same throughout the Tertiary in all northern lands, and since the climax of Cenozoic vulcanism came as early as the Miocene, the importance of this factor in impoverishing the Pleistocene life of the western part of the United States may be questioned. Furthermore, it has little or no application to Europe, where the flora was equally reduced. The to-and-fro movements of the land faunas and floras must have introduced an elaborate series of superpositions, giving an elaborate, orderly, and unusual succession. The record of this succession has not been worked out in its completeness, and unfortunately there is little chance that it will be worked out in its fulness unless by the most persistent care. In the regions which were glaciated repeatedly, the advance of each ice-sheet destroyed, in most places, the record of the successive floras and faunas which had lived since the preceding retreat, so that, within the area glaciated, the succession of successions is hardly likely to be found in its entirety in any one place, and perhaps not in all places. Outside the area which was glaciated, especially near the borders of the regions occupied by the successive ice-sheets, there is better chance that a complete record of the biological changes may have been preserved. ‘The peat bogs of such regions might be expected to give complete records if they had endured continuously since the time of the first glaciation; but peat bogs are themselves temporary, and it is perhaps too much to expect that complete record of the migrations of life during the successive epochs of the glacial period will ever be found at any one place. The records, however, of the post-glacial peat bogs are such as to give some indication of the results which would probably be found if all the migrations could be ascertained. Thus in Scandinavia and Denmark, we have a succession of post-glacial floras, the first cor- responding in a general way to the present vegetation of the tundra, the second a forest vegetation dominated by the birch and poplar, the third a forest vegetation dominated by pines, the fourth, one dominated by the oak, etc., the fifth a flora similar to that of the Black Forest Mountains, indicating a temperature warmer than that of today for the same region, and finally, a southward retreat of the 274 ROLLIN D. SALISBURY last flora to its present latitude. The first five members of the succes- sion seem to correspond with the half of a normal interglacial series. If this interpretation is correct, this series of five floras would be nearly doubled with the on-coming of another glacial epoch, and this doubled series must have been repeated, substantially, several times in the course of the long succession of glacial epochs. Fragments of inter- glacial records have been found both in America and Europe. Ina few cases they are full enough to encourage the hope that when their number is duly increased, they may be pieced together into consistent wholes. It is too much to expect that they will ever be as complete as the record of post-glacial life. It is not now apparent just how far biologic or paleontologic data of the Pleistocene, except for their record of climatic changes, are to be significant in correlation. Aside from the mammals, changes of species have been insignificant. Even among mammals, it is not clear that the dying-out of species in one locality was contemporaneous with the disappearance of the same species in other localities. A stratigraphic basis for this interpretation would be needed before it could be accepted. So far as all other forms of life are concerned, the paleontologic record of one interglacial epoch must have been essentially identical with that of another, if the intervals were equally long and mild. Perhaps more help in correlation may be looked for in another direction. Intercontinental migrations, it would seem, must have been virtually restricted to interglacial epochs. The times when species first appeared in a given region may therefore prove to be much more significant in correlation than the times when species died out. Something perhaps may be hoped for in the careful study of the records of oscillations of level, during the period; but it seems clear that different parts of the same continent have suffered minor or even considerable deformations, independently of others. If it were established that opposite sides of an ocean basin were less independent in this respect—a doctrine for which much might be said—the movements on opposite sides of an ocean basin might be a hopeful line of research; but it cannot, at the present time, be said to have led to important conclusions. PHYSICAL GEOGRAPHY OF THE PLEISTOCENE 275 It would appear that only through a combination of stratigraphic, climatic, paleontologic, and orogenic studies, carried out in greater detail than they have yet been, can important results in the correla- tion of Quaternary formations be reached, between widely separated areas. PALEOGEOGRAPHIC MAPS BAILEY WILLIS U.S. Geological Survey 15. QUATERNARY NORTH AMERICA North America during the Quaternary presents very unusual features. The land area is large. The margin of the continental plateau is now somewhat submerged, but probably has not been so throughout the period. Marine embayments are not extensive, except Hudson Bay, which is a fair example of the smaller epi- continental seas that have spread over various parts of the continent in the past. Mountain systems that are great in extent and height have grown from the places of the early Tertiary ranges of the Cordil- lera, which had been deeply eroded before the Pliocene. ‘The Appalachian Mountains, which began to rise above the plains of eastern America possibly as early as the Eocene and which toward the close of the Miocene had ceased to grow at something less than half their present greatest height, have been raised to their existing altitudes during the Quaternary. These mountain features of North America are paralleled or exceeded in other continents and the period is thus characterized as one during which the forces that raise mountains have been decidedly active. In late Tertiary time great differences of climate developed. The equatorial, temperate, and polar zones became much more unlike than they ever had been, according to the geologic record. The Quaternary is distinguished by the development, the advances, and retreats of several ice sheets, whose combined areas are shown on the map. ‘The expanse of ice was at no one time so great, but the entire area shown as ice was covered at one time or another, and some parts of it several times successively, by continental glaciers. The developments of topography and climate, including polar refrigeration and corresponding modifications of oceanic conditions, have greatly changed the environment of plants and animals, and have resulted in special phenomena of competition and adaptation, through which existing forms have been evolved. 276 pi SS WSS | Hy APHIC MAPS ~ mA C PALEOGEO Ay Taw LALLA yi oy ih hl TAN ! MY | fii Mn it WH ‘ LA a) 1 Hy the ‘y iy cy i } Wi tit ERICA POLAR EQUATORIAL Ss S Ss ARINE WATER SA ate ecetes °°, SSeS 2 < nn 50 % NORTH AM EANIC BASIN NDS CLUDING MARINE SEDIMENTS M CONTINENTAL DEPOSITS, SOMETIME LA MARINE CURRENT } CHAPTER XV ORIGINATION OF SELF-GENERATING MATTER AND THE INFLUENCE OF ARIDITY UPON ITS EVOLUTIONARY DEVELOPMENT D. T. MACDOUGAL Any attempt at an interpretation of a desert landscape, with its diversity of forms, isolation of individuals, and scarcity of organic matter in the soil, leads inevitably to a consideration of the theoret- ical conditions which would be necessary in the origination of the physical basis of life, its development into organisms known to us in the living and fossil state, and also of the possibilities of the oc- currence of a re-generation at the present time. From almost every excursion which the biologist has made into this inviting field of speculation on which he has called to his aid various extreme or unusual intensities of the factors to be taken into account, he has been ruthlessly recalled by the geological historian with the reminder that the general composition of the atmosphere, its pres- sure, the temperatures, and other conditions prevalent on the earth’s surface were uniform and continuous with those now encountered and not widely different, in their total departure, in any stage of terrestrial development in which life might have originated. Now we are not able to discover that living or self-generating matter is actually being formed anew on the earth’s surface at the present time, and in the absence of positive evidence we are com- pelled to say that all life now in existence must have descended from forms which had their ultimate origin in other times and under other conditions than those now prevalent. A consideration of the phyletic aspects of fossil and living forms of plants yields but little, which might serve as an indication of the conditions under which the earlier forms developed. Even the earliest remains include such advanced types as the ferns and cycads. The amount of progress represented by the derivation of the gameto- petalous seed-plants from these, in comparison with the preceding 278 ORIGINATION OF SELF-GENERATING MATTER 279 evolution, is quite insignificant, while even the simpler forms of animals and plants are to be considered as types widely divergent from primitive self-generating matter, being removed from it by the slow but sure advances of untold millions of years of development. It is, therefore, as if we had observed the events and objects of yesterday and were called upon to read the history of the past cen- tury. In the search for supporting ideas upon which to base specu- lation, two conceptions serve as encouragement for a renewed attack upon this fascinating problem. One is embraced by Chamberlin’s planetesimal theory of the growth of the earth and the attendant modification of surface conditions, which necessarily showed a com- plex widely different from the present, and the other is one, growing in favor with physiologists, to the effect that the essential activities of living matter rest upon catalysis, and enzymatic processes, with the characteristic reaction velocities directly affected by internal and external limiting factors. The protamic nucleus may be taken to represent the first form in which self-generating matter might be said to have the characters of protoplasm, but previously to its synthesis there must have occurred an increasingly complex series of carbon compounds, with hydrogen, oxygen, nitrogen, sulphur, and phos- phorus, while iron, calcium, magnesium, and potassium are also involved in its activities at the present time. ‘That these main con- stituents were present in the atmosphere at partial pressures of varying intensity, and that unstable carbides, nitrates, phosphides, and sulphides brought by infalling planetesimals were passing into more stable unions with the formation of hydrocarbons, ammonia, hydrogen phosphide, etc., is suggested by Chamberlin, and the possible interactions and combinations might result in the synthesis of very complex substances, well up toward the simpler forms of living matter. The hypothesis formulated by him also assumes that the surface of the earth was unworn piled talus, but little of which had gone into solution. The development of the hydrosphere moistening this layer, and forming pools and small bodies of water all exposed to the light of the sun, together with the variations in temperature, partly due to the heat of impact of infalling bodies, the influence of magnetic fields induced by bodies circulating about the earth determining the paths of ions and electrons traversing them, 280 D. T. MACDOUGAL and other states of ionization, due to radioactivity, would all be possible factors contributory to a synthesis that might form a beginning of the physical basis of life. Any resulting thermo- catalyzer would be a possible agent for self-organization, and in the development of an organic type its characteristic activities would consist in the degradation, or reduction of the potential energy of the medium or substratum and the oxidation of the acquired substances. Living matter is in fact a thermal engine in which the oxidation is, comparatively, exceedingly slow. Fic. 1.—Mud-volcanoes of Lower California, in and around which unusual oppor- tunities for chemical combination are offered by the’ conditions of temperature and pressure. No process observable by available physiological methods sug- gests the origination of living matter, yet it seems quite probable that combinations similar, analogous, or even identical with the earliest forms might be produced in the laboratory, in inclosed spaces or under special conditions. Doubtless compounds of much greater intricacy have been made, but while we might make such substances, yet it would be extremely difficult for us to furnish the supply of material and the continuance of conditions which would permit this matter to exercise its initial functions of self- generation to any appreciable extent. The starting of a strain of ORIGINATION OF SELF-GENERATING MATTER 281 living matter which might perpetuate itself and evolve into differen- tiated forms will long remain one of the most difficult feats which confronts the experimenter. The tests and criticisms which have been applied to the results of the few essays that have been made for the production of bodies which would be self-maintenant in a suitable medium, have been, for the most part, misdirected. ‘Thus in the consideration of the hitherto unsuccessful efforts to produce bodies simulating some of the properties of self-generating matter, tests for the physical and chemical properties of protoplasm as well as for phenomena of the cell have been applied, regardless of the fact that the cell probably stands removed by a million years of evolution from the simple living material which first took shape, and represents, in fact, simply a successful form of organism and by no means the only possible morphological organization. Such misuse of criteria has doubtless operated to curb research and discourage experimentation, and while it may have seemed soundly conservative for Kelvin to say: But let not youthful minds be dazzled by the imaginings of the daily news- papers that because Berthelot and others have thus made foodstuffs they can make living things, or that there is any prospect of a process being found in any laboratory for making a living thing... . . There is an absolute distinction between crystals and cells. Nothing approaching to the cell of a living creature has ever yet been made,? yet the actual accomplishment of self-generating matter is, as sug- gested above, a theoretical possibility in the laboratory. The pro- vision of a proper nutritive environment would present greater difficulties than the construction of a thermo-catalyzer capable of sustaining itself in a proper medium. After growth and decay, the next most important property of living matter is that of irritability, of impressibility, and of accommo- dation to environment. The basic substance of protoplasm endured because of a capacity for withstanding the current range of tem- perature and insolation, and this endurance was made possible by fairly automatic adjustments, one of the simplest of which is encoun- tered in recognizable form in living plants today in the decrease of water content, consequent upon the cooling of protoplasm. Few 1 Nature, XXXI, 13, 1904. 282 D. T. MACDOUGAL adjustments are so simple, and, of course, more complicated ones became possible as atomic group after atomic group was added to the constituency of living matter. Along with these acquisitions the feature of the rhythmic action which has become so characteristic and important for the living growth is to be considered, and this with contractility is dependent upon surface tension, viscosity, etc. . So far the properties suggested are those common to all living forms, but there must have ensued many differentiations of living matter, of which we have two survivals in plants and in animals. It seems probable that the first specialization resulted from the forma- tion of substances in some of the living masses which converted radia- tions of certain wave-lengths into heat and other forms of energy active in promoting the reduction processes. A fortuitous move- ment toward such specialization may indeed have been the factor that made for survival in an environment of decreasingly avail- able supply of chemical energy. The highest development of this power of absorption of light rays is to be assigned to chlorophyll, but preceding the formation of this very intricate and unstable sub- stance there may have occurred a series of other compounds acting as heat-absorbent screens, of which the reddish and bluish pigments of the lower algae are surviving examples. Many disintegration products constituting the reds and blues of plant tissues sustain physical relations of a similar character to sunlight. It is not possible to formulate any rational conception of living mat- ter without including its environmental relations. These become of the utmost importance at the moment of formation of self-generating matter, and it may be assumed with perfect safety that of all the pos- sible synthetic processes only those which ensued in the presence of a medium which furnished substances suitable for building material could survive. Furthermore, when the accumulation of this material and its specialization is considered it is apparent that successful origination occurred only on solid or semi-solid substrata rather than in undifferentiated solutions in open waters. Still an abundance of this liquid would be of great importance to the colloidal masses which we may think of as the earliest living things, and, as will be shown presently, water has continued to be the most important of all of ORIGINATION OF SELF-GENERATING MATTER 283 the things affecting development especially with regard to the vegetal organism. The first method of multiplication of individuals or colloidal masses undoubtedly consisted of simple fragmentation resulting from the accumulation of a mass too great to be held together by surface tension, and the separation of these masses must have been accomplished, or made possible by flotation which continues to be one of the most efficient agencies in the dissemination of plants, a fact specially emphasized by the results of our studies upon the revegetation of the Salton Basin. An early specialization of structure probably rested upon the reduction of portions of the self-renewing colloidal masses from the suspended condition of a sol to the condition of a gel, and doubtless the limiting membranes of protoplasmic masses depend upon this process. Likewise some form of centrum resulted from congelation processes by activities of a nature elementary to the relations of the nucleus and cytoplasm in the modern cell. Wherever portions of the colloidal mass came into contact with solid substances gelation or aggregation ensued, and the masses of material thus differentiated would give form and stability in place, representing the earliest form of anchorage organ. In this as well as in other features of the plant, evolutionary development was slow so long as the monotonous conditions of an aquatic habitat were to be met. Very simple processes or extrusions from a cell or coenocyte of this general nature are still to be encountered among certain algae. As soon, however, as it was left stranded by the disappearance of the shallow waters in which it may have lived, or was lifted above the water level by any means, the diversified conditions encountered by the organism, including desiccation, exercised a differentiating effect on the root-organ scarcely less marked than those which may be ascribed to the same agency in the shoot. The necessity for anchorage was no less, but now the nutritive substances no longer bathed the entire body but were present only in hygroscopic solutions on the soil particles with a vertical distribution not uniform, and with much horizontal irregularity. Survival depended upon the formation of specialized tracts for absorption, and conduits for the transport of solutions from the organ of fixation to other parts of the living mass. It is to be noted, however, that the modern root arose anew from the 284 D. T. MACDOUGAL vegetative axis, and is therefore not directly derived from the primi- tive anchorage organs described. The present occasion does not warrant a discussion of the evolu- tionary development of the vegetal organism from the colloidal mass to the gametophyte, now represented by the prothallium of ferns and their allies. Neither is it necessary to recall details of plant anatomy further than to point out that the earlier forms of plants, co-ordinately with the monotonous conditions offered by their ac- quatic habitats, showed no differentiation of tissues comparable with that of the axis of the modern seed-plant, and that their flattened bodies were for the most part closely appressed or adherent to the substratum. ‘The development of the sexual type of reproduc- tion in such forms had been followed by a habit of formation of the sexual organs separately, perhaps some distance apart on the upper or lower surfaces of the body. In the functionation of such organs the two kinds of protoplasts representing the sexual elements would be set free at the surface of the body and accomplish union while swim- ming freely, or in higher stages of development, the one representing the egg-cell would remain in place, while the fertilizing protoplast, or spermatozoon would find its way to it. In either case free water was absolutely necessary for reproduction. The body of the plant might be partially or completely immersed, or it might have only a thin film coating the surface, through which the sexual elements must move, but in either case the plant could not survive away from the margins of streams, seas, and lakes, or up out of the moist lowlands, or beyond the borders of rainy regions. The thallose forms carrying on sexual reproduction do not appear to have been capable of the morphological development which might have gained them independence from the water, and this freedom was gained only after a secondary, asexual generation came into existence. In the general movement which finally resulted in a land flora, the fertilized egg held in the body of the thallus would germinate in place, developing into a vegetative structure (the sporophyte) unlike the thallus which bore the egg. Then cells were cut off, or separated from the body of this alternate generation, known as the sporophyte, which had the power of developing into thalli like the ORIGINATION OF SELF-GENERATING MATTER original. 285 Now the germination and growth of these asexually pro- duced spores could proceed in the absence of free water, and in ordinary soil in which all of the water present was represented by the hygroscopic layer coating the minute particles of which it is com- posed. Even with this development, however, plants could not get very far from the water, since this ele- ment in a free state was still neces- sary for the activities of the gameto- phyte, or sexual generation. The sporophyte, however, continued to increase in size and to wax in importance in the life-cycle of the species, until finally its body was much larger than that of the gametophyte. ‘This feature is well illustrated by the tree ferns in which the sporophyte is a massive plant while the prothallium, or sexual generation, is a small thallose structure only a few millimeters across. Eventually, however, the spores formed by the sporophyte, capable of living on dry land, were germi- nated in place, giving rise to sexual individuals, which were also held and nursed in the tissues of the sporophyte. Then in completion of the movement, accessory struc- tures, including the pollen-tube, were formed, by which the sexual Fic. 2.—The gametophyte, or sexual generation of a fern. Reproduction is accomplished by the movement of a sperm (a) from the antheridium A to the archegonium B where it fuses with the egg, accomplishing fertilization. The sperm swims through a thin film of water which may be present. ‘The absence of the film by aridity is unfavorable to the reproduction and continuation of this type of vegetation. The germination of the egg produces the sporophyte or fern plant ordinarily known (see Fig. 3). reproductive elements might be brought together independently of external conditions. By these steps the seed-plant originated and vegetation became truly and wholly able to occupy the land—a most 286 D. T. MACDOUGAL momentous change, and one of great importance in connection with the general subject under consideration. Temperatures alone have been unduly drawn upon in the inter- pretation of distributional features of ancient and existing floras, a fact made more plainly apparent by recent observations at the Desert Laboratory, in which it has been found that several species range over a vertical mile. Such species endure cold of — 35° C. and have a growing season of less than a hundred days in the more boreal or alpine portion of their ranges, while in the southern or lower locali- ties inhabited by them, temperatures of 48° C. may be encountered; the growing season extending over 300 days; the thermometer going below the freezing-point not more than 12 hours during the entire year. It is with no surprise, therefore, that it is learned that there is no single feature in the structure and functionation of plants that with perfect assurance may be connected with the influence of tem- perature alone, although alpine and polar floras bear a distinct aspect by reason of a combination of conditions of moisture, insolation, duration of the seasons, and course of the humidity. While temperature is not in itself a direct factor in shaping the general trend of evolutionary development in plants, yet it is indi- rectly concerned by the influence exerted upon precipitation, and the relation of the amount of the rainfall to the possible evaporation. The great changes in the climatic pattern of the surface of the earth, both in this and preceding periods, produced by whatever cause, may be taken to have affected vegetation chiefly through the humidity and desiccation effects, which not only determined the range and habitats of the species, but also played a predominant part in shaping the general development of the vegetal organism. It will be profitable therefore to analyze the changes accompanying a modification of a climate toward or away from the desiccation of a region and the response of the flora to such altered conditions of environment. ‘To do this most effectively let us suppose that the rainfall in New York, Pennsylvania, Labrador, Iowa, or Florida were reduced to one-fourth of the present amount by a gradual decrease through a long term of years. In the lower levels of the region affected, the total production of organic matter would be ORIGINATION OF SELF-GENERATING MATTER 287 greatly lessened and consequently the amount of humus would decrease; wind erosion would remove much of this from its place of formation and by this means alone the distribution of many species would be totally altered. The soil moisture would ultimately be so depleted that the surface layers would show as great a proportion as the underlying layers, carrying an excess during seasons of precipi- tation, a fact that would have the profoundest influence upon the native vegetation, determining not only the habit of the root-systems, the form of the shoot, but also becoming a factor in distribution, and giving a new form to the competitive struggle among the organ- isms in a locality. The change in precipitation would result in the formation of long outwash, detrital slopes, or bajadas, giving new habitat conditions, and a further differentiation would consist in the surface accumulation of soil salts, giving alkaline and saline areas upon which halophytic, or saline plants flourish. The lessened relative humidity would result in modification of foliar surfaces, make necessary for survival special structures in seeds and spores, and would be followed by a more intense insolation by reason of the non- absorption of some portions of the spectrum, and lastly the course of the temperature of the soil would change with the depletion of the humus and the altered water relations. If desiccation ensued as a result of simple horizontal reduction of the precipitation, in a region with an unbroken surface lying at nearly the same level, the effect would be sweeping, monotonous, and with an almost total absence of selective effect that would mean extermination, or change in a flora en bloc. The majority of inter- pretations of the paleontological record assume such results. It is to be seen, however, that desiccation in a region with diversified topography and great differences in level would result in great differ- entiation, and if to this reduction is added the restriction of the rain- fall to one or two brief seasons or to limited periods a maximum of effect may be expected. The development of desert conditions in the manner described over a region of any extent would entail the least disturbance on mountain summits, where, by reason of the lowered temperature and the facilities for condensation, the evaporating power of the air would remain lowest. The original, or pre-desert forms would be able 288 D. T. MACDOUGAL to maintain themselves on such elevated slopes with but little adjust- ment. Similar survivals might ensue along the lower drainage lines, where the underflow in streamways and washes might support a moisture-loving vegetation as it does in southwestern Africa and southwestern America. So much for survival by localization. A second manifestation would be shown by restriction of seasonal activi- ties. The rate of evaporation on the lower levels might be lessened by lower temperatures during the winter season and at this time rapidly acting annual plants might carry through their cycle of activity, remaining dormant in the form of heavily coated seeds during the warmer, dryer period of the year. Perennials with deciduous leaves might display a coincident activity. This survival of moisture- loving plants in a region of pronounced desert character is most marked, however, in places where the precipitation occurs within definite moist or rainy seasons, such as the great Sonoran desert in which two maxima of precipitation occur, separated by periods of extreme drought. Both the winter and the summer rainy seasons are characterized by the luxuriant growth of broad-leaved annuals, which might not be distinguished from those of any moist region. Some species are active during the summer season, and others during the winter, while a smaller number perfect seeds during both seasons. A number of perennials parallel this activity of the annuals with the result that in the most arid parts of Arizona, according to the unpublished researches of V. M. Spalding, half of the native species are in no sense desert plants, requiring as much moisture for their development as do those of Maryland, Michigan, or Florida. The desiccation of a region is seen therefore not to result directly in the extermination of moisture-loving types, but rather to the reduc- tion of their relative or numerical importance and a limitation of their activities to limited periods, or moist seasons. Two types of vegetation may be definitely connected with arid conditions, representing as they do the morphogenic action of water which has been a predominant one in the development of the seed-plants. In one form the chief operation has been one of reduction and protection of surfaces. Leaves have been reduced to linear vestiges representing various parts of the foliar organ, branches to spines or short rudiments as in certain Fouquieriaceae, Fic. 3.—(Above) Tree-fern in a moist tropical forest in Jamaica, in which such plants survive. (Below) Dense carpet of borages and other annuals which grow from seed during the rainy season in the Tucson desert. These plants are similar in habit and structure to those of a moist region. 290 D. T. MACDOUGAL stomata show special constructions, and all parts of the shoot heavily coated and hardened; root-systems have been extended horizontally and the individuals thus isolated, being more or less accommodated to soils containing a large proportion of salts. The spinose, stubby, and switchlike perennials which result from such action are char- acteristic of low, inclosed desert basins, like the Salton, and those of southern Africa, and central Asia, where the scanty rainfall does not occur within such regular limits as to make distinct moist seasons. The second form of desert vegetation is one in which the absorp- tive function has become highly developed and the capacity gained for conserving the surplus water taken up during the moister seasons. The Cactaceae are the most prominent representatives of this type in North America, and some of this group, as well as other species representing a wide range of families, have the capacity for sufficient water to meet the needs of the individual for a decade, while forms are known which might carry out their cycles of reproduction for a quarter of a century by the use of the surplus accumulated within their bodies. Such succulents display not only the reduction of the shoot and of the foliar surfaces together with induration of the epidermis, but have also this capacity for accumulating water and are hence desert plants par excellence, representing the apex of specialization to desiccation. As a total result of the slow desiccation of any region, therefore, a very important proportion of the flora would consist of moisture- requiring species, or mesophytes, and the remainder would be included in two classes, the spinose forms with reduced shoots and roots, and the succulents with atrophied shoots, but with the addi- tional development of storage structures in some organ of the shoot or root. The total number of species within an arid region is not less than that of the most densely closed tropical area, but the num- ber of individuals is less, the interrelations of the individuals and species are not identical, and the competitive struggle for existence Is of a nature widely different from that of a tropical forest. Increase in aridity tends to localization in distribution, and increase in humid- ity to diffuseness. Evidence of the existence of xerophytes in previous periods of desiccation is extremely scanty. Calamites and lycopods with a ORIGINATION OF SELF-GENERATING MATTER 291 slender central cylinder and a thick inclosing cylinder of thin- walled tissue have been alluded to in this connection, but these great Fic. 4.—Aspect of the vegetation in regions with no well-marked rainy seasons of regular recurrence. (Below) The bolson of Las Vegas, Nevada. (Above) Bajadas of minor range of mountains near the shore of the Gulf of California, San Felipe Bay. The plants comprise spinose forms with very reduced shoots and leaves, which have not developed storage capacity. sporophytes probably stood in swamps, or at least were hygrophytic in habit, and by the requirements of their separated gametophytic 292 D. T. MACDOUGAL reproduction could not exist on land areas independently. It is also to be noted that many forms peculiar to swampy areas at the present time display reduced shoots and leaves of a specialized structure due to the action of certain constituents in the substratum, that they are known as ‘‘swamp xerophytes” and if brought to light as fossils might give the impression of having lived in an arid climate. Fic. 5.—Types of plants from the Tucson desert, where two distinct yearly periods of maximum precipitation occur. In addition to the morphological reduction of the shoots and leaves, the capacity for the accumulation and retention of water has reached an enormous development. A group of sahuaros (Carnegiea gigantea) on the left; a single bisnaga (Echinocactus Wislizenii) on the right. The last-named plant has a supply sufficient for a dozen years’ activity in its tissues. The leaves of conifers very probably represent a specialization adapted to existence in a dry atmosphere, yet it is notable that the greater majority of surviving species live in soils in which the occur- rence of moisture is not that of the desert. The swollen stems of the Bennettitales offer the strongest sugges- tion of desert forms, and their structure and reproduction would ORIGINATION OF SELF-GENERATING MATTER 293 make possible their maintenance as independent inhabitants of the dry land. It is true, of course, that desert conditions are not favorable for fossilization, yet many opportunities for such action undoubtedly occur in the carrying and burying action of the torrential floods of desert streamways, while wind-blown deposits might preserve the more indurated forms. Many of these and the skeletons of the Cactaceae would seem well adapted for preservation in this manner, although no remains have yet been uncovered. The view that such forms are of recent origin, within the present period of advancing desiccation, would predicate a very great phylogenetic activity unpre- cedented perhaps, but by no means impossible. The actual relationship between plants and their environment is by no means a settled question and since this and related problems are to be discussed in detail at the Darwin memorial session of this meeting, this subject will not be considered here farther than to say that it is unsafe to asssume that any organism has undergone adap- tation and fitting specialization in direct somatogenic response to any set of environic factors, and that admissible evidence on such matters is extremely difficult to obtain.! The operations of factors lessening the supply of water to any region would of course result in greater aridity in some places than in others and the movements of xerophytic forms established in these to other contiguous areas dried out later would be a matter in which the direction of the winds, streamways, movements of animals, and position of mountain barriers would play a determin- ing part. The recession of large expanses of water included in a desiccating region, such as has occurred in the great basins in Utah and Nevada, and in the bolsons to the southward and eastward in New Mexico, Chihuahua, and Arizona would present special conditions. The rate at which the waters of such inland seas might recede, however, would be such that the advance of vegetation to cover the immersed areas would be quite as rapid as that necessary to follow a receding ice- sheet or a change of climate due to any cause. Thus our observa- tions on the Salton Lake show that beaches a mile in width are bared 1 Fifty Years of Darwinism. New York: H. Holt & Co., rgo9. ® 204 D. T. MACDOUGAL within a year, while the agencies most effective in their revegetation are combined wind action and flotation. Many areas, such as the central basin of Asia, the American desert, the Eyre Basin in Australia, and southern Africa, offer clear examples of the effect of desiccation upon the vegetation of a region, but when we proceed to the consideration of the probable happenings when an arid region receives an increasing precipitation, our speculations must be based wholly on experimental evidence of the physiological behavior of plants under known conditions. Here, as in the decrease of the supply of water, no mass move- ment or extermination of a flora is to be taken for granted. Many highly specialized succulents extremely local in their distribution would undoubtedly quickly perish with the progression of a climate bringing an excess of moisture; alterations in temperature would not exercise such violent action upon plants of wider range, however. That both together might not totally exterminate a type of succulent is shown by the existence of cacti in tropical rain-forests and on the high northern plains of Nevada, Idaho, and Montana. If plants of wider latitudinal distribution are taken into consideration it may be seen that with an advance of polar climate to the southward the extermination of a species in the northern part of its range would be coincident with additions to the eligible area on the southward. If the land area were limited or if mountain barriers intervened, such dissemination would of course be impracticable and the forms involved would soon perish. These features must be taken into account in an interpretation of the flora of the inclosed basin of central Asia, which, so far as the meager information available shows, is extremely poor in the higher succulent desert types, a characteristic also of the Death Valley and of the Salton Basin in North America. The unfavorable influence of increasing moisture upon the xerophytic forms of a region would also include effects of an indirect character. Soil temperature and moisture relations would undergo great alterations, humus would increase, and other changes would ensue, entailing conditions which their specialized structures would be unfitted to meet. Furthermore, succulent and spinose plants being advanced types, their retrogressive evolution to conform to ® ORIGINATION OF SELF-GENERATING MATTER 295 moist conditions would be a process resulting in enormous loss of species. Some spinose types would seem to offer the best morpho- logical features for such a change. Perhaps the most inportant of all of the altered conditions brought about by increasing moisture, however, would be the total trans- formation of the competitive struggle for existence. Animals would no longer play the predominating role as in arid areas. The num- ber of individuals representing the constituent species of a flora would be multiplied a hundred fold, perhaps a thousand fold, and once more the amount of food material offered to animals would decrease their total importance as a factor in selection, while the intensest crowding between shoots would once more be resumed and horizontal differentiation of associations such as that in forests would ensue. The element of a desert flora which would respond most readily to ameliorated aridity would, of course, be the hygrophytic annuals and perennials, which had survived the period of desiccation in their refuge of the rainy seasons, and in the moist areas along stream- ways and on elevated peaks. ‘These would quickly occupy the greater part of the surfaces available for plants to the great intensification of the inter-vegetal struggle for existence. As these hygrophytes survived in the moist situations and the moist seasons of an arid period, so the surviving xerophytes in a moist period would find refuge in restricted habitats on talus slopes, rocks, and sand in which the soil-moisture relations would be best suited to their specialized structure and might display their seasonal activity during a period of the year in which the precipitation was least. Briefly restating the principal ideas touched upon, it may be said that Chamberlin’s prothesis of the planetesimal aggregation of the outer portions of the earth and the attendant conditions, together with current theories as to the catalytic nature of the essential activi- ties of protoplasm, makes possible rational speculations upon the origination of self-organizing matter. The passing of nitrates, phosphides, carbides, and sulphides into more stable combinations might readily result in the formation of thermo-catalysts, one type of which survived in the later forms of living matter. Similar combinations do not appear to be taking 296 D. T. MACDOUGAL place at the present time, and their accomplishment experimentally is attended with difficulties not yet surmounted. The part of the evolution of living matter which may be brought under observation in living forms or preserved material represents very advanced stages and the cell is separated by a wide range of development from the colloidal masses in which self-generating matter first took form. The construction of substances which might use or transform energy other than that of chemical structure represents the first differentiation between the animal and vegetable organisms. Plants were necessarily confined to aquatic or hygrophytic habitats as long as their history included the free gametophyte, and a land flora became possible only with the development of the sporophyte culminating in the derivation of the seed-plants. In this and in subsequent history the water-relation has played the predominating morphogenic role. The desiccation of a region occupied by a land flora would entail a complex series of changes in climatic and other environmental factors which may be followed by extermination or differentiation of the flora. This differentiation, which would ensue most readily in regions of diversified topography, with an absence of barriers preventing distributional adjustments, would include localizations of habitats, seasonal restriction of activity, and transformation of the competitive struggle for existence from one chiefly among plants to one between plants and animals. The surviving flora would include an important proportion of mesophytes or hygrophytes, while the arid conditions might be followed by the development of two types of xerophytes, succulents, and spinose forms. The amelioration of desert conditions would mean a reversal or shifting of various environic factors, the whole favoring the increase in the number of individuals representing the mesophytes, the widening of their habitats, and the institution of the fiercer compe- tition among plants. Such changes would force a retrogressive development on the xerophytes, exterminating many, restricting the range of all, and would result in the survival of a few under con- ditions wholly foreign and antagonistic to those in which their characteristic qualities originated. ORIGINATION OF SELF-GENERATING MATTER 297 In all attempts to correlate ancient floras and interpret the climate of formations, especially with regard to aridity, the following features are to be taken into account: Vegetation of diverse lower types might cover moist lowlands, make a profuse growth along streams, or clog extensive stretches of shallow waters in seas and lakes, but only seed-plants could occupy dry land. It is to be borne in mind that the forms represent- ing this advanced type must have constituted a small proportion of the vegetation for a long period after their origination. Their present predominance must be a very modern feature. Furthermore, the dissemination of new forms proceeds somewhat slowly and it is by no means to be taken for granted that the existence of seed- plants, as denoted by fossil remains, is to be taken as an indication that such plants occupied or covered great continental areas. Soil conditions would be a very important factor in such distribution. The distinction between the vegetation of a region in alternating moist and arid epochs may not easily be made, since as has been pointed out the fossilization of the flora of the Arizona Sonora desert would probably result in material richer in moisture-requiring plants than in xerophytes The morphological features of the forms pre- served would offer the most valuable evidence, and the presence of a single xerophyte among a hundred forms requiring moisture would be of great significance. The final stages in the differentiation of the land flora, by which spinose and succulent xerophytes have come into existence, seems to have been reached within very recent times. No fossil remains of desert plants have yet been recovered. Some of the forms which have the aspect of xerophytes must have grown in moist regions by reason of their method of reproduction. Some of the cycads and the conifers may be regarded as being most suitable of the older types for existence under arid conditions. The fitness of these plants is due almost wholly to features of the shoot, and the known features of their root-systems offer nothing suggestive of adapta- bility for the characteristic soil conditions of the desert. CHAPTER XVI DIASTROPHISM AS THE ULTIMATE BASIS OF CORRELATION THOMAS CHROWDER CHAMBERLIN The University of Chicago There are many and diverse views relative to the nature and the causes of diastrophic movements. To keep as largely as may be on common ground, most of these divergencies of view may be set aside as immaterial to our present purpose. We may all agree that the fundamental factors of the case are a lithosphere with a deformable surface, a liquid, covering part of this surface and determining erosion and sedimentation, and a gaseous envelope. We may easily agree that the outer part of the lithosphere is solid and has a sufficient measure of rigidity to maintain the surface inequalities. I do not see that we need to agree as to the causes of deformation. In some sense, I do not see that we need even to agree as to just what the absolute movements were, i. e., I do not see that it is material for us here to know whether the deformative movements were shrink- ages, or expansions, or lateral shifts, provided we agree as to the general nature of their effects on the agencies at work on the surface of the lithosphere. We do not need to entertain the same conception of the nature of the earth’s interior, if we are at one as to the working conditions which have prevailed on its surface. No doubt we can easily agree on the present great working factors: (1) abysmal basins occupying about two-thirds of the earth’s surface, bordered by terrace faces rising at angles of 2° to 5° for say 12,000 feet to a quite definite terrace-angle about 1oo fathoms below the sea-level; (2) continental platforms whose upper faces slope gently up from this angle to the coast-line and thence ascend into the various reliefs of the land. If we thus agree that the upper face of the conti- nental platform is bounded by the edge of the continental shelf, and that this edge is equally the boundary of the abysmal basins, whether the waters overlap the edge or not, we may also agree that 298 DIASTROPHISM AS BASIS OF CORRELATION 209 the edge of the oceanic waters, whether they agree with the edge of the abysmal basins or not, form the chief line of demarkation between the great erosions and the great depositions the world over. It is not the only line of such demarkation, to be sure, for degradation gives place to aggradation at many other local horizons, but in this discussion let us agree to deal only with factors of the larger order and to neglect incidentals; let us deal with body deformation, rather than local or provincial warpings. We all recognize further that the sea-level is not only a dividing plane between two great divisions of physical agencies, but between two great biological divisions. To this list of agreements, there are two other propositions which we cannot add quite so unhesitatingly, because we need to weigh them well, and if we cannot all agree respecting them, we must agree to differ, for they are fundamental to the further discussion. These relate to the effects of body deformation on the relations of land and sea. If deformation were confined to the abysmal bottoms and were compensatory, no effect would be felt on the relations of land and sea. If deformation were confined wholly to the interior of the continents, it would be similarly ineffectual. Deformations so limited are, however, likely to be only provincial, and fall outside our discussion. There remain two conceptions of general or body deformation between which choice must be made. In the one, the deformations are supposed to be indifferent to their predecessors, and to disregard the configurations produced by previous deformations. Their suc- cessive effects upon continental outlines and basin capacities are thus heterogeneous and the combined results irregular and uncertain. It is not clear to me how they can be made a very trustworthy basis of systematic correlation. ‘The submergent phase of one continent or fraction of a continent may, in this case, be contemporaneous with the emergent phase of another continent or fraction of a continent, and the progress of events on one continent is as likely to be contrasted with those of another continent as to fall in with them co-ordinately. According to the other view, deformations are inheritances, one of which follows another in due dynamical kinship. The succession is therefore homogeneous and the results co-ordinate. If, for example, 300 THOMAS CHROWDER CHAMBERLIN the first depression of the abysmal basins was due to the superior specific gravity of the basin-bottoms, this specific gravity remained and participated in the next deformation. If the continental masses, at the outset of continental formation, were relatively low in specific gravity, this low specific gravity was handed down to later periods and helped to renew deformation of the same phases in the same regions. Under this view, ocean basins and continental elevations tended toward self-perpetuation. It is not assumed that this prevented shell crumplings, provincial warpings, or block movements of diverse phases within the continental or the abysmal areas, for these might obviously be necessary effects of the general deformative movements, or at least inevitable incidents connected with the dynamics lying back of them. A choice between these two conceptions is imperative to this discussion, as they lie at the parting of the ways in the interpretation of the larger events of geologic history. I accept the second view with much confidence. It should be more fully qualified respecting the incidental accompaniments just mentioned, but time does not permit. According to this view, each great diastrophic movement tended toward the rejuvenation of the continents and toward the firmer establishment of the great basins. The distinction between con- tinent and basin must not, however, be interpreted on the super- ficial ground of the water-line, for the water-line merely shows that the basin is over-full, just full, or under-full, as the case may be. The average water-line undoubtedly helps to give a definite terrace border to the abysmal basin, but the water-line freely abandons this and often is far from coinciding with it. The base-leveling processes have shown that they are able to lower the continents approximately to the sea-level in a fraction of geologic time. ‘The continents would therefore have long since dis- appeared, if they had not been rejuvenated by renewed relative elevation or the withdrawal of the sea. J am able to find no evidence of lost continents. There are submerged margins, and matter has been carried continent-ward from denuded borders. There are some submerged dependencies and _ inter-continental connections. There are also some rather deeply submerged ridges that probably DIASTROPHISM AS BASIS OF CORRELATION 301 connected the present continents at remote stages in their history. In the earlier eras, when the differentiation of platforms and basins was less advanced, ridges which have since been submerged are perhaps recognizable. In the interpretation of the earlier periods, these should probably be restored as continental connections. In the earliest known ages, these may have been rather numerous and their combined area considerable, but these seem to me to be only qualifying features which, by the natural place in evolution which they fill, support, rather than weaken, the general conception of a systematic succession of deformations in which the offspring of each is the parent of the next, and in which both continents and ocean basins were progressively segregated and unified. I trust that many of you will agree that, in general, the relatively upward movements of diastrophism have been located continuously in the continents, and the broad downward movements continuously in the ocean basins, and that, setting aside incidental features, the dominant effect of the successive diastrophic movements has been to restore the capacity of the ocean basins and to rejuvenate the con- tinents. This conclusion seems to me to be strongly supported by the general course of geologic history, wherein sea-transgressions and sea-withdrawals have constituted master features. Perhaps our firmest ground for this conviction is found in the present relations of the continents and the sea basins. If heterogeneity had dominated continental action in the great Tertiary diastrophisms, the results should stand clearly forth today. Some continents should show recent general emergence, while others should show simultaneous general submergence. The dominant processes today should be those of depressional progress, on the one hand, and those of ascen- sional progress, on the other. As a matter of fact, all the continents are strikingly alike in their general physiographic attitude toward the sea. They are all surrounded by a border-belt, overflowed by the sea to the nearly uniform depth of 100 fathoms. ‘These submerged tracts are all crossed by channels, implying a recent emergent state. None of the continents is covered widely by recent marine deposits, and yet all show some measure of these. Wide recent transgressions in one part do not stand in contrast with great elevations in another. Even beyond what theory might lead us to expect, when we duly 302 THOMAS CHROWDER CHAMBERLIN recognize the warpings incidental to all adjustments, the recent rela- tions of the continents to the seas conform to one type. The 10,000,000 square miles of continental margin, now submerged, is distributed around the borders of all the continents with a fair degree of equability. May we not, therefore, agree that in the world-wide phases of diastrophic movements, the basins have been additionally depressed and the continents repeatedly rejuvenated. It is important that we should agree, or agree to disagree, on one further point. Have diastrophic movements been in progress con- stantly, or at intervals only, with quiescent periods between? Are they perpetual or periodic ? The latter view prevails, I think, among American geologists. This view has acquired especial claims since base-leveling has come to play so large a part in our science, for it is clear that the doctrine of base-leveling is specifically inconsistent with the doctrine of perpetual deformation, for the very conditions prerequisite to the accomplishment of base-leveling involve a high degree of stability through a long period. The great base-levelings, and the great sea-transgressions, which I think are little more than alternative expressions for the same thing, have, as their fundamental assumption, a sufficient stability of the surface to permit base-leveling to accomplish its ends. Shall we not therefore agree that there has been periodicity in the world-warping deformations? Let this not be held with such exclusiveness that we fail to recognize duly the effects of the adjustment of minor stresses, at other times. ‘These may be preliminary or after-effects of the larger movements, or they may be due to local stresses more or less independent of the general body-stresses. These quite certainly have been present, and have produced intercurrent departures from the strict tenor of the great systematic movements. If there is need for additional argument on periodicity, it may be found in theoretical considerations, but these we have tried to avoid in the main. Whatever we may regard as the fundamental agencies that give rise to those stresses in the earth which are precedent to deformations, we may easily all agree that the earth opposes some resistance to deformation. ‘There is certainly some rigidity in the body of the earth. According to the fundamental laws of rigidity, the deforming stresses must reach a certain magnitude before a DIASTROPHISM AS BASIS OF CORRELATION 303 movement can start. Now, if we recall that every such deformative movement, affecting a free surface, in its very nature, throws the resisting crust into an attitude of relative weakness, it follows that, with such progressive easing, the movement will go on until the stress is accommodated and a state of equilibrium essentially restored, after which another period of accumulation is prerequisite to another movement. If we are agreed on the periodicity of great deformations, it clearly follows that in a quiescent state the base-leveling of the land means contemporaneous filling of the sea basins by transferred matter, and hence a slowly advancing sea-edge which is thus brought into active function as a base-leveling agent. This water movement is essen- tially contemporaneous the world over, and is thus a basis for corre- lation. The base-leveling process implies a homologous series oj deposits the world over. At first these represent the conditions imme- diately following continental rejuvenation. Later they are succeeded by the deposits representing the modified conditions to which the first stage gives rise, and so on through the series up to the climacteric ones when base-leveling has reached its greatest development. After this a declining series follows. The deposits of the more advanced stages of base-leveling are, as now well recognized by most American geologists, markedly different in physical constitution and physio- graphic aspect from those of the earliest stages of continental rejuve- nation. The criteria for discrimination between these earlier and the later members of the series are indeed of the collective rather than the individual type; they have character as distinctive assemblages of criteria rather than as single or isolated criteria, but they are perhaps all the safer for this composite character. Correlation by base-levels is one of the triumphs of American geology; correlation by its complement, transgressive deposits on a base-level, may easily be added, and perhaps on quite as firm or even firmer physical grounds. If we add the biological element the case is immeasurably strengthened, for correlation by cosmopolitan faunas, the very best of faunas for the purpose, is added to the physical correlation. Migration at the climax of base-leveling and sea- transgression is freer and more prompt than at other times. Corre- lation to the foot, as by an unconformity, may not be practicable, but 304 THOMAS CHROWDER CHAMBERLIN the precision of correlation by unconformities has more apparent than real value, for the different parts of the same unconformity vary much in time. All distant correlations involve some measure of inexactness, and the more frankly it is made obvious, the less its liability to mislead. Correlation by general diastrophic movements takes cognizance of four stages: (1) the stages of climacteric base-leveling and sea- transgression, (2) the stages of retreat which are the first stages of diastrophic movement after the quiescent period, (3) the stages of climacteric diastrophism and of greatest sea-retreat, and (4) the stages of early quiescence, progressive degradation, and sea-advance. (x) The characteristics of the climacteric stage of base-leveling and sea-transgression need little further characterization here, for the function of base-levels is known to all American geologists and the function of great sea-transgression to every stratigrapher and paleon- tologist. We have in base-leveling conjoined with sea-transgression, just that combination of agencies which is competent to develop the broad epicontinental seas of nearly uniform depth requisite for an expansional evolution of shallow-water life. At the same time, it furnishes broad pathways around and across the continental surfaces for wide migrations and the comminglings that lead to cosmopolitan faunas of the shallow-water type. (2) The stages of initial diastrophism and sea-retreat find their criteria in the deposits that spring from an increased erosion of the deep soil-mantles accumulated in the base-level period, in the effects of increasing turbidity, in the lessening areas suitable for the shallow- water life, and in the limitation of migration. (3) The climacteric stages of diastrophism are marked by the stress of restrictional evolution among the shallow-water species; by increased clastic deposition in land basins, on low slopes, and on sea borders, by great land extension, but often, perhaps dominantly, by diversity of land surface and by liability to climatic severities and diversification. Areally, land life is favored, but it is hampered by the climatic and topographic diversities, and these may prove graver obstacles to migration and intermingling than even the tongues of sea that previously traversed the land surface. Correlation by glaciation in these stagessis likely to prove a valuable adjunct, but we DIASTROPHISM AS BASIS OF CORRELATION 305 must first test our criterion, for we are not as yet quite sure that contemporaneity of glaciation is inferred on reliable grounds. The shallow-water life of the diastrophic stages is driven into narrow border tracts and into local embayments, and is thus forced into special adaptations and into narrowly provincial aspects. (4) The early stages of quiescence and of base-leveling, with advancing seas, are peculiarly fruitful in biological criteria, for they are marked by re-expansions of the narrowly provincial shallow- water faunas of the previous stages. The progressive development of these provincial faunas and their successive unions with the faunas of neighboring provinces, as these come to coalesce by means of the progressive sea-advances, form one of the most fascinating chapters in life evolution, and give some of the most delicate of criteria for correlation. This rough outline is quite too meager duly to set forth the criteria of correlation connected with the stages of general diastrophism. It rather suggests them than sets them forth. It remains to consider the precedence among themselves of the three factors, diastrophism, deposition, and life development. We are accustomed to look to the life record as our chief means of correlation. Its very high utility is quite beyond discussion. Thoughtful students, however, recognize that the paleontological record is based, in an essential way, on stratigraphy and that it is corrected and authenticated by the precise place the life is found to occupy in the stratigraphical succession. Stratigraphy and paleon- tology thus go hand in hand, each sanctioning the other. Dzastro- phism lies back of both and furnishes the conditions on which they depend. ‘The relationship is not reciprocal in any radical sense. The life does not, in any appreciable way, affect diastrophism. Deposition has been thought to be related to mountain-folding. Erosion in one area and deposition in another has been assigned as an initial agency in deformation. While some influence of this kind may be conceded, I think it is rather a localizing influence than a fundamental one. If wrinkling must take place from other causes, quite possibly previous erosion here and deposition yonder may localize the wrinkling. But that is quite apart from fundamentally causing the wrinkling. Reasons are prowang yearly in cogency why 300 THOMAS CHROWDER CHAMBERLIN we should regard the earth as essentially a solid spheroid and not a liquid globe with a thin sensitive crust. I think we must soon come to see that the great deformations are deep-seated body adjustments, actuated by energies, and involving masses, compared to which the elements of denudation and deposition are essentially trivial. Denu- dation and deposition seem to me clearly incompetent to perpetuate their own cycles. It seems clear that diastrophism is fundamental to deposition, and is a condition prerequisite to epicontinental and circum-continental stratigraphy. Diastrophism thus seems to me fundamental both to stratigraphic development and life development. Diastrophic action seems to be the forerunner of both these standard means of correlation. It there- fore seems to be the ultimate basis of correlation. ‘The criteria of this correlation include at once its own specific criteria, the criteria of stratigraphy as dependent on diastrophism, and the criteria of paleontology as modified by the direct and indirect effects of diastro- phism. Re IN ge era Pa Cy Ge he Ay Ns ae ee : . | a , 4 ae , 7