BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA V o l..¿5, pp. 325-340 September 15, 1914 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY

CRETACEOUS-TERTIARY BOUNDARY IjST THE ROCKY MOUNTAIN REGION1

BY P. H . KNOWLTON

(Presented before the Paleontological Society December 31, 1913)

CONTENTS Page Introduction...... 325 Stratigraphic evidence...... 325 Paleobotanical evidence...... 331 Diastrophic evidence...... 334 The European time scale...... 335 Vertebrate evidence...... 337 Invertebrate evidence...... 339 Conclusions...... 340

I ntroduction The thesis of this paper is as follows: It is proposed to show that the dinosaur-bearing beds known as “Ceratops beds,” “Lance Creek bieds,” Lance formation, “Hell Creek beds,” “Somber beds,” “Lower Fort Union,”- Laramie of many writers, “Upper Laramie,” Arapahoe, Denver, Dawson, and their equivalents, are above a major unconformity and are Tertiary rather than Cretaceous in age. As this is essentially a stratigraphic problem and not, as some assume, an exclusively paleontologic one, a certain amount of structural data are necessary as a setting for the paleontology. It is proposed, therefore, first, briefly to present the evidence on which this unconformity is predi­ cated. S tratigraphic E v id e n c e The geological formations here involved are spread widely over the States of New Mexico, Colorado, Wyoming, the Dakotas, Montana, and

1 Manuscript received by the Secretary of the Geological Society June 14, 1914. Contribution to the symposium held at the Princeton meeting of the Society Decem­ ber 31, 1913, and January 1, 1914. Published with the permission of the Director of the U. S. Geological Survey. (325)

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adjacent Canadian territory. It is held that the dinosaur-bearing beds above mentioned are separated from underlying beds by a major uncon­ formity which makes the logical line of separation between Cretaceous and Tertiary. In eastern Montana, eastern Wyoming, and the Dakotas, where far removed from the influence of the Rocky Mountain uplift, the forma­ tions involved arc approximately horizontal. In a majority of cases within this area the dinosaur-bearing Lance formation appears to rest conformably on the underlying beds, and it is this condition apparently which has led many observers to deny the possibility of the existence at these points of a time interval of any importance. It needs but a mo­ ment’s reflection, however, to show that because one formation lies in apparent conformity on another, this is not of necessity proof positive that the process of deposition continued uninterruptedly from the begin­ ning of the first to the close of the second. It may often happen that we must go outside the area where such ap­ parent conformity obtains for the evidence which shall not only prove the existence of the stratigraphic break, but also the value of the hiatus. It happens, however, that even in the flat-lying beds in the Dakotas there is some evidence of the measure of this time interval. The maximum thickness of the Fox Hills—the formation beneath the Lance—is given as 450 feet, yet in; many places it is 75 feet or less, and in exceptional cases appears to be entirely absent, and the Lance then rests on Pierre. An element of caution is necessary in interpreting this condition. Ine­ qualities in the thickness of a formation of the well known character of the Fox Hills may be due to erosion or to irregularity of original deposi­ tion. That this unequal thickness in the Fox Hills is actually due to erosion and not to irregularity of deposition is indicated in at least two ways: First, by the finding of actual erosion surfaces, as, for instance, the one described by Calvert on Grand River, South Dakota, where within a horizontal distance of 500 feet there is an observed vertical cut of at least 72 feet, and other similar occurrences in western North and South Dakota and eastern Montana, and, second, by the difference in the invertebrate fauna in the lower and upper portions of the full Fox Hills section, which is approximately 1,000 feet in thickness. In the type sec­ tion of Fox Hills at Fox Ridge, South Dakota, the beds show a thickness of only about 325 feet. The fauna in this type section is said to show more or less of a commingling of Pierre forms, and for this reason it was at one time the inclination to abandon the use of Fox Hills as a distinct formation and to regard it as merely a near-shore phase of the Pierre. Where the full 1,000-foot section of Fox Hills is present, as in the Denver

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basin of Colorado, it appears, according to Dr. C. A. White, that the invertebrate fauna in the upper portion, while it contains some of the species of the lower portion, is on the whole distinct. This is taken to indicate that the full section of Fox Hills is nowhere present in the Da- kotas, and that the incomplete development of the formation here is to be ascribed to removal of the tipper part by erosion rather than to diminished rate of sedimentation or to stratigraphic overlap. In Worthless Creek Valley, South Dakota, the pre-Lance unconformity is angular as well as erosional, the Fox Hills dipping north at an angle of 4 degrees, whereas the overlying Lance is horizontal. On the Moreau River, near Govert post-office, South Dakota, the Lance is horizontal, while the underlying beds dip northwest at an angle of 10 degrees. At a number of points in the eastern part of Custer County, Montana, the Lance rests on a distinctly eroded surface of the Fox Hills. Likewise, according to Barnum Brown, the same condition obtains on Hell Creek, in Dawson County, Montana. Throughout much of Montana and Wyoming the conditions are the same as those above described, namely: The Lance is found resting on Fox Hills of different thicknesses, often with eroded surface, and in some cases, as at Forsyth, Columbus, etcetera, the Fox Hills is entirely absent and the Lance rests on Pierre and not always on its uppermost member. It has been suggested that in those cases where the Lance rests directly on Pierre the lower sandstones of the Lance may be the fresh-water phase of the Fox Hills. Proof of this contention would be the finding of an area in which there is evidence either of a transition laterally from the purely marine conditions of the Fox Hills through brackish water to the suggested fresh-water facies of the “Lance,” or a barrier separating two such areas of deposition on which neither facies was laid down. If the country within which the Lance is found resting on Pierre was one in which the stratigraphic relations were obscure on account of few or poor exposures, such transition or barrier might possibly have escaped detection; but on the contrary it is a region in which exposures are numerous and ample, and moreover is one in which investigation in recent years has been intensive, but no such condition has been observed. In the cases thus far considered the discordance between the Lance and underlying beds is not always evident, nor is it always conspicuous when present, and hence it is held by some geologists to be of no more importance than unconformities acknowledged to be present at various horizons in the Lance. The essential difference lies in the fact that the unconformities within the Lance are obviously local and can be traced only for short distances, whereas the evidence in support of the pre-Lance

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interval is cumulative, since it occurs at the same horizon throughout four great States. Of much greater significance, however, is the fact that this pre-Lance interval marks the boundary between the last of the under­ lying series of chiefly marine Cretaceous beds and the succeeding exclu­ sively continental deposits which prevailed thereafter in the Rocky Moun­ tain area. In other words, with a single exception this boundary marks the final retreat of the marine waters from the Rocky Mountain province. The most complete measure of this pre-Lance unconformity is to be found in the vicinity of the mouth of the Medicine Bow River, in Carbon County, Wyoming. This unconformity was first detected and studied by A. C. Veatch in the vicinity of the town of Carbon, which is about 25 miles south of the Medicine Bow River. Veatch holds that this time interval represents the removal of more than 20,000 feet of strata. The horizon below this unconformity was called “Lower Laramie” by Veatch; but it is now regarded by the writer as the true Laramie,, while the hori­ zon above was called “Upper Laramie,” now, in the writer’s opinion, proved to be the dinosaur-bearing Lance formation, since it contains the remains of Triceratops. The line then recognized as the boundary be­ tween these two formations was structurally correlated northwest to the vicinity of the mouth of the Medicine Bow River, and thence up that stream for a distance of some 25 miles above its junction with the North Platte. According to Ball, at a point about 20 miles above the junction the “Upper Laramie” and irLower Laramie” were found in contact with marked angular discordance. During the present field season [1913] C. P. Bowen, of the United States Geological Survey, found remains of dinosaurs 1,000 feet or more below the horizon at which Veatch, in his reconnaissance work, had drawn the line between his “Lower Laramie” and “Upper Laramie.” On account of the lithologic similarity of the rocks of this region, careful areal work may be necessary before the line can be drawn exactly. The line taken by Doctor Peale and the writer as that of the major uncon­ formity may prove to be only one of the minor breaks known in the Lance, in which event Bowen’s discovery merely reduces the supposed thickness of “Lower Laramie” rocks from 6,000 feet to 4,000 or 5,000 feet. On the other hand, indeed, it may be possible that dinosaurs act­ ually occur in the “Lower Laramie,” 2 since they undoubtedly existed somewhere at this time, but none properly identified have as yet been found in undoubted Laramie.

3 Since the above was written Bowen has informed me that the only dinosaur found in the lower part of the so-called “Lower Laramie” is about 700 feet above the top of the Lewis shale and 100 feet or more lelow a horizon containing Halymenites. This shows that probably it is not in the "Lower Laramie” at all, but in the Fox Hills unit, which in that area is mapped with the “Lower Laramie” !

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Another fact of importance may be pointed out regarding this Medi­ cine Bow region, namely: Bowen reports that he has found dinosaurs at a number of horizons that are from 300 to 500 feet above the top of the "Upper Laramie” as fixed by Yeatch. This shows the extent of the ver­ tical range of the dinosaur fauna. In North Park, Colorado, the upper plant-bearing beds are apparently the same as those in Carbon County, Wyoming, as the two areas are closely connected, and from there it is but a step to the Denver basin of Colorado, where Whitman Cross demonstrated the presence of the great unconformity which separates the dinosaur-bearing Arapahoe and Den­ ver formations above from the Laramie beneath. The Laramie is here reduced in thickness to about 1,600 feet, and at Colorado Springs, 75 miles south of Denver, which is the southernmost point at which Lara­ mie is known, the thickness is reduced to 425 feet. W. T. Lee; has shown to the satisfaction of many that the full Cretaceous section, to and in­ cluding the Laramie, was laid down uninterruptedly over the area where the Bocky Mountains now exist. As the most complete section believed to represent the Laramie—namely, near Carbon, Wyoming—has a thick­ ness of 5,000 feet, and as the Laramie in the Denver basin is only 425 to 1,600 feet thick, it is an indication that the unconformity may have rer moved at least 4,000 feet of beds and probably it was very much more; in fact Cross’s estimates places it at 12,000 to 15,000 feet. Between the Denver basin and Colorado Springs is a series of arkosic beds to which the name Dawson arkose has been given. The Dawson rests with marked discordance on all underlying beds, and is shown by its stratigraphic relations and contained flora to be the time equivalent of the Denver and Arapahoe formations. The Dawson contains abun­ dant remains of dinosaurs, and in direct association with them Richard­ son found a mammal bone which Gidley pronounces to be characteristic­ ally Creodont, and says: “From our present knowledge the type repre­ sented could not be older than Wasatch.” This association of dinosaurs and mammals is obviously of importance. In the Raton Mesa region of southern Colorado and adjacent New Mexico, W. T. Lee has also demonstrated the presence of the same great unconformity, which by actual measurement has removed over 6,000 feet of beds and probably it was much more. Lee has also demonstrated the presence of the unconformity of many points around the southern end of the Rocky Mountains and up along the western base to southern Colorado. In this Raton Mesa region the beds above the unconformity, called the Raton formation, are not known to be dinosaur-bearing; but they do contain an ample flora, which is correlated with the Denver and

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Dawson to the north, and to the south with the Eocene Wilcox formation of the Gulf region. The Wilcox formation is underlain by the marine Midway formation, at the base of which is the Tertiary-Cretaceous line of the Gulf coastal plain. This post-Cretaceous hiatus has now been traced over a wide areal ex­ tent from the Canadian border to New Mexico, and it has been definitely tied in with a marine section in the Gulf region. It has been shown to occupy the same relative position throughout, and we are now in position to measure its magnitude. It appears to have involved at least the re­ moval of the full thickness of Pox Hills and Laramie, where the maxi­ mum thickness of Fox Hills is 1,000 feet, and the thickest known section of Laramie is about 5,000 feet, or a total of 6,000 feet that may have been removed. It is not now known whether in Montana, eastern Wyo­ ming, and the Dakotas the Laramie and the full Fox Hills section was ever deposited; but it seems certain to me that the pre-Lance hiatus is the time interval during which they were deposited in various areas and subsequently removed in whole or in part. Suppose, for the sake of argument, we deny the validity of this uncon­ formity as a criterion for establishing the Cretaceous-Tertiary boundary. Where, then, shall this line be placed? Take first the Lance formation. Tt is now established beyond question that the sedimentation was con­ tinuous and uninterrupted3 from the beginning of the Lance to and through the Fort Union. At the hundreds, even thousands, of localities where the two occur in the same section it has been found absolutely im­ possible to draw any satisfactory line between them on structural or lithologic evidence. The Lance is not mapable as distinct from the Fort Union. In one of the latest publications of the United States Geological Survey,4 which covers a very large area in eastern Montana, the two are mapped together, for, as W. R. Calvert, its author, says: “As a result of these conditions [outlined above] no attempt is made on the index map, or on the maps of the various areas treated in this report, to differentiate the Lance formation from the overlying strata described in connection with the Fort Union form ation an d he continues, “The lowest persist­ ent lignite bed was in the field arbitrarily considered to be the upper limit of the Lance;” . . . and he concludes. “It cannot be emphasized too strongly that the upper limit adopted is merely suggestive, as the finding of Triceratops bones higher in the section will necessitate the upward extension of the formation.” It would seem that a geological system ought at least to be a mapable unit!

3 Except possibly in the Cannonball region of North Dakota, which will be considered later, and within a single township in the Bighorn Basin of Wyoming. ‘ Bull. 471, I'. S. Geological Survey, 1912, p. 25.

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The vertebrate paleontologists apparently would place the top of the Lance at the highest point at which dinosaurs have been found; but unfortunately in those areas—and there are very many of them—where no dinosaurs are known the Lance will be without a known top, and even where they do occur this sliding scale makes the fixing of the boundary dependent on the accident of discovery, and the point accepted as the line today may be very different from that necessitated by the work of tomorrow. The invertebrate paleontologist would fix the top of the Lance by the highest point at which marine invertebrates have been found. This cri­ terion is even more limited in its application than the last, since marine invertebrates are known from a comparatively small area in North and South Dakota. It is obvious, therefore, that the fixing of this boundary lias a practical aspect that must be considered, as well as the technical, stratigraphio. and paleontologic sides. If we subordinate the taxonomic significance of this pre-Lance datum plane as certain paleontologists would do, we sub­ stitute for it a criterion of vague, obscure, and unequal application. “Next to natural relationship the quality of convenience is the prime desideratum in stratigraphic taxonomy,” says Ulrich in discussing the Ordovician-Silurian boundary; and he continues, “Let us, then, be rea­ sonable and practical and accept with proper valuation these diastrophic boundaries, which nature has most clearly and widely indicated.”

P a h ko n o r a n ic a l K v i ijk x c k I am possibly prejudiced when T say that to my mind the paleobotanical evidence is convincing and of the highest importance. First, as to the evidence it affords regarding the distinctness of this time break: In the Raton Mesa region the Vermejo formation, the first beneath the unconformity, has a flora of 108 species. The Raton forma­ tion, the one next above the break, has a flora of 118 species. Only four species have been found in common. In the Denver basin the Laramie has a published flora of 97 species, six of which are found also in the Raton flora and 10 in the Arapahoe and Denver floras. Tn Carbon County, Wyoming, the “Lower Laramie” (true Laramie, in the writer’s opinion) has a flora of about 50 species, five or six of which occur also in the dinosaur-bearing beds above, which has a flora of about 70 species. Throughout the vast area over which the Lance formation is known there have been reported 16 species of plants that come into its flora from beds below the unconformity—that is, from the Laramie, Montana, etcetera. On eliminating the duplications in these several lists, as well as the

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few forms now known to have been incorrectly identified, we have a total of only 21 or 22 species that are known to have crossed the line of the unconformity. The full significance of this small number is brought out when we aggregate the floras in the beds below and above the uncon­ formity. In the lower beds—that is, Vermejo, Laramie, Montana, etcet­ era—there are 350 species, and in the upper beds—Eaton, Dawson, Arap­ ahoe, Denver, Lance, etcetera—there arc over 700 species. Twenty-one or 22 species in common with 350 below and over 700 above is an insig­ nificant number. It shows that more than 90 per cent of the Cretaceous flora was wiped out by the disturbances attending this diastrophic move­ ment. The length of this time interval is indicated bv the flora in another way other than in the destruction of the species. I f the flora in the beds above the unconformity was wholly or even largely of a different type from that in the beds below, it might mean that it had come in suddenly, “ready made,” from an adjacent area, without great lapse of time; but as a matter of fact it is in the main a continuation of the Cretaceous flora, and its evolution from the Cretaceous remnants implies a considerable length of time. We may now consider the paleobotanical evidence regarding the corre­ lation, age, etcetera, of the formations here involved, beginning with the area where our knowledge is most complete and passing over the ground in a reverse order from that in which the structural relations were dis­ cussed. By common consent the physical break is made the basis of the separa­ tion between the Cretaceous and Tertiary in the Atlantic and Gulf coastal plain. In the Gulf region the Cretaceous Selma chalk and the Eocene Midway formation are on opposite sides of the line, and both are of marine origin. In a paper recently read before the Geological Society of Washington, Dr. L. W. Stephenson stated that the hiatus between the Cretaceous and Tertiary represented a longer time, regarded as due to evolutionary development, as measured by the change in life forms, than is indicated by the full Upper Cretaceous section of the region. Above the Midway formation is the Wilcox formation, which is also marine except in the Mississippi embayment. The Wilcox contains a published flora of about 65 species, of which number about 25 are found also in the Raton formation. But Mr. E. W. Berry is engaged in the preparation of an elaborate monograph of the Wilcox flora, in which he will enumerate over 300 species, not one of which, by the wav, has been found in the Cretaceous anywhere. Less than 80 of its species have been found outside of this formation. Between 30 and 40 species are now

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known to be common to the Eaton and Wilcox formations, and when Mr. Berry’s work is available it will be found that there are probably not less than 50 common or closely related species. Mr. Berry is of the opinion that the Wilcox may be slightly younger than Ihe Raton, and it may he that it is the equivalent of the upper part or perhaps the whole of the Midway, as well as a portion of the Wilcox. This correlation of the Raton formation with the Wilcox and Midway is important, since it ties the Rocky Mountain section with the marine section of the Gulf, where the geologic relations are definitely known. This correlation was first pointed out by Lesquereux more than 40 years ago, when he had at his disposal only a handful of specimens from either area, and it is a pleasure to attest its correctness, which is not changed, with the fullest collections ever brought together for any Rocky Moun­ tain aiea. The Raton formation, as already indicated, contains a flora of 148 species, only four of which are known to occur in the Yerniejo formation immediately below. This flora is especially characterized by vast num­ bers of palms, some with leaves 6 or 8 feet in diameter, and is rich in figs, cinnamons, magnolias, bread-fruit trees, etcetera, and indicates a moist, warm, possibly subtropical climate. The Raton formation is cor­ related by its flora, as well as by its stratigraphic relations, with the Denver formation of the Denver basin. The latter—the Denver—has a published flora of 98 species, over 40 per cent of which are common to the Raton, and there is a large mass of unworked material, which when elaborated will undoubtedly increase the number of species common to these two formations. The Arapahoe formation has a flora of 32 species, nearly all of which have been found also in the Denver. The flora certainly lends support to the view that they are not greatly different. On the south and southeast of the Denver basin is the area occupied by the Dawson arkose, which, as already stated, is believed to be strati- graphically continuous with the Denver and Arapahoe formations, the difference between them being largely lithological, the Denver being ande- sitic and the Dawson arkosic. The flora of the Dawson numbers between 30 and 40 species, nearly all of which are typical and well known Denver species. There can be no doubt, therefore, that the two are of the same age. The correlation of the Denver and the Raton is also well attested by the flora. The plant-bearing beds in North Park, Colorado, may next be consid­ ered. There is very little topographic relief within this area, with the result that exposures of the strata are few and usually poor. The coa.1-

XXIV—B u l l . G e o l . S o c . A m ., V o l . 25, 1913

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bearing and plant-bearing beds appear to rest on marine beds perhaps as old as the Mancos, the Laramie, so far as known, being absent. The flora in these beds, although small, is undoubtedly the same as that in the “Upper Laramie” near Carbon. Dinosaurs have not been found in North Park, though they are abundant in the beds in Carbon County, Wyoming. The flora of the “Upper Laramie” in Carbon County embraces about 70 species, of which number nearly one-half are common to the Lance of other areas, and there are also large unworked collections that will prob­ ably still further augment the number of common species. As already indicated, five or six of these species are known in the underlying “Lower Laramie.” We have now come to the consideration of the flora of the Lance. I have already shown that the Lance formation is inseparable—structurally and Iithologicaliy—from the overlying Port Union, and the flora is like­ wise so markedly of Fort Union facies that it is often quite impossible to distinguish the one from the other without stratigraphic or other data. As the Tertiary age of the Fort Union is admitted by every one, it is not necessary to dwell on this point. It has a large flora of perhaps 500 species, many of which are still undescribed. The Lance flora embraces about 100 named and described species, as well as a considerable number not yet described. Of these 100 species,.over 75 are typical Fort Union species that have never been found in older beds and most of them only in the Fort Union. I am, of course, well aware that statistics may mean little or much, depending on how they are compiled—that is, the mere presence of a species in a list may have little significance or real value. In the present case, however, many of these Lance species are found at dozens of localities and often in hundreds of individuals. To any one familiar with the Fort Union flora, its prepon­ derating element in the Lance flora is apparent. The evidence regarding the post-Cretaceous floras has now been pre­ sented for the vast area which extends from Few Mexico to Alberta. It lias been shown that in the south the Eaton formation is to be correlated with the marine Eocene of the Gulf region, and step by step the correla­ tion through the Dawson, Denver, and Lance has been traced until it merges inseparably with the Fort Union, which is of acknowledged Eo­ cene age.

D iastrophic E vidence I had hoped to be able to present certain diastrophic evidence, which I consider of the highest importance, if any serious attempt is to be made in settling the Cretaceous-Tertiary boundary, but it has been deemed

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inexpedient to discuss this at the present time. I may only say, there­ fore, that we are not concerned with the various theories as to why the earth changes its form, but simply that it does do so, which is unques­ tioned. That these changes or crustal movements are periodic in their action is also evident, and, moreover, it is possible to demonstrate a cer­ tain amount of rhythm in these activities. That is to say, while some of these movements have obviously been more or less local in their action, others have been not only continent-wide, but practically and simultane­ ously world-wide. These grand periods of diastrophic activity, which have been variously called “revolutions,” “critical periods,” or “grand cycles” in the history of the earth, have long been recognized and ac­ cepted by most geologists. According to Ulrich, there have been at least four such major periods of activity on the North American continent, the latest important one being the one here involved, namely, at the close of Cretaceous time. The Cretaceous was a period of maximum sea extension throughout the world, and its close was marked by maximum sea exclusion. According to Schuchert’s paleographic maps of North America, the Cretaceous Sea was spread over a wider continental area than had previously been occu­ pied by marine waters since perhaps Silurian or Devonian time. The Eocene witnessed the sea withdrawal in Europe as well as in North America.

T h e E uropean T im e S cale This is perhaps an opportune point at which to consider the so-called European standard and to compare it with the American conditions and requirements. In this connection I must express my indebtedness to Mr. W. T. Lee, who has spent much time in consulting the literature. It is recognized that the subdivision of stratified rocks into systems is imperfect. Probably no system is completely represented in any one place. It is recognized that the type locality of a system may not contain its fullest expression as to range and age. Hence a type standard—such, for example, as the European standard—is at best only temporary, since it was based on incomplete information and must eventually give place to a standard of world-wide application. It is, therefore, obviously unwise to set up a European standard for measuring American systems, as if that standard were final. I say a European standard rather than the European standard, for there are disagreements among Europen geolo­ gists as to the line of separation between Cretaceous and Tertiary just as there are in America. In order to answer the question “How does the European standard aid

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in drawing the line of separation between the Cretaceous and Tertiary in America?” it is necessary to go back and determine at several critical points what constitutes this standard. The Cretaceous and Tertiary systems were worked out in the Anglo- Parisian basin. The type area of the Cretaceous—or Chalk, as it was called until 1822, when d’Halloy introduced the term Cretaceous for it— is in the London basin, and the Tertiary was first worked out near Paris. Geikie says, concerning them, that both in France and in England “the lithologic sequence, being the more obvious, was first established before it was confirmed and extended by a recognition of the value of the evi­ dence of organic remains.” This statement, that the systems were estab­ lished on a physical basis, is abundantly verified by the early writings. As the systems were studied in other regions, conflict of opinions devel­ oped as to the position of the Danien and Montien beds, which seem to contain a mixture of Cretaceous and Tertiary forms. Some of the Eu­ ropean geologists place these formations in the Cretaceous, others in the Tertiary, while Dollo, Haug, and others assign the Danien to the Creta­ ceous and the Montien to the Tertiary. It is significant that, although several fossils of Cretaceous type occur with those of Tertiary type in the Montien, Haug reverts to the original criteria for determining the sepa­ ration between the two systems, and places the Montien in the Tertiary because it lies unconformably on the older rocks. In his summary of the Montien, Haug states that it contains, together with Tertiary forms, several survivors of the Cretaceous faunas, among which are crocodiles, magalosaurs, and other dinosaurs. Two things mentioned above are especially significant: (1) The Cre- ceous and Tertiary systems were originally established on a physical basis, and the exact line of separation between them was determined by the structure; (2) after more than a century, during which the several lines of evidence have been tested, the last authoritative word on the European standard is to the effect that the structure is the determining factor in separating them, and that even dinosaurs, that have been appealed to so often as proof of Cretaceous age, did not end with the Cretaceous. Probably all American geologists will agree as to the desirability of conforming the American geologic time scale as closely as possible to the European standard, and probably all who have thought seriously on the subject will also agree that it is impracticable, perhaps impossible, to do so in all cases. “I do not hesitate to express the opinion,” said the late Dr. C. A. White,6 “that it [the European standard] is not of infallible

5 Proc. Amer. Assoc. Adv. Sci., vol. 38, 1889, p. 225.

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application to other parts of the world, except perhaps as to its larger divisions, and that even in this respect it will need modification.”

Vertebrate E vidence

I shall have very little to say regarding the vertebrate evidence. If the presence of dinosaurs is to be taken as prima facie indication of Creta­ ceous age, then this discussion might as well end at once, for it is beyond question that dinosaurs are present in beds above the unconformity which, in my opinion, separates Cretaceous from Tertiary. Vertebrate paleontologists have claimed that the dinosaur fauna of the Lance, Denver, etcetera, does not give any indication of this time break, thereby implying that there is a dinosaur fauDa immediately below the unconformity which can be directly compared with the Ceratops fauna. But is this true ? So far as known to me, from field observations and a study of the literature, dinosaurs have not been found in the beds which immediately underly the unconformity—that is, in Laramie, Pox Hills, uppermost Pierre, etcetera—except possibly in Alberta and below the Puerco formation, where the relations are in doubt. The nearest dinosaur fauna with which that of the “Ceratops beds” can be compared is in the Belly Eiver, which is stratigraphically some 2,000 feet below the unconformity, and when we make this comparison we find, I am told by Mr. Gilmore, that not a single species, and perhaps only a single genus, is common to Belly River and “Ceratops beds.” The Ceratops fauna, therefore, proves clearly that there has been a very dis­ tinct change in passing over the line of the unconformity. A word may be said regarding the Edmonton of Canada, which has been, supposed to be the same as the Lance formation of the United States. According to Barnum Brown, the dinosaur fauna of the lower portion of this formation—the so-called lower Edmonton—is distinctly more primitive than that of the Lance, being in fact much more closely related to that of the Belly River. In one of his later papers, dealing with this field, Mr. Brown has announced his intention of establishing a new formation for this lower Edmonton; but until the full data, strati­ graphie as well as paléontologie, have been published it is perhaps useless to speculate, further concerning the fauna. I may say, however, that Mr. Brown has kindly permitted me to study the fossil plants of the Edmon­ ton section, and I have found them, with the following exception, to be uniformly of Port Union or Lance types. The collection from 16 miles below Tolman, in beds stated on the labels accompanying the specimens to be lower Edmonton, is distinct from anything before submitted to me.

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This lot contains a Ginkgo nearest to and probably identical with Ginkgo laramiense Ward, from Point of Eocks, Wyoming, a cycad—Pterophyl- lum—©f a type not found above the Cretaceous, and two species of dicoty­ ledons; Viburnum, an unpublished species from Point of Eocks, and Platanus wardii ? Kn., from the lower Montana of the Missouri Eiver below Coal Banks, Montana. In my opinion, this collection has a distinct Cretaceous aspect, though it is obviously too small to predicate positively its age. This may explain why the fauna exhibits such an evident affinity with that of the Belly Eiver. I am forced to the conclusion that two very distinct horizons may have been confused under the name of Edmonton. It is just possible that this may be the long lost Laramie fauna. This issue can not be avoided, as Doctor Matthew and others have pro­ posed doing, by extending the definition of Laramie from a formation to a group, for then we shall not only contravene the original definition, but we shall have the anomalous condition of the “Laramie group” being divided by a major unconformity and falling within two systems. The original pronouncement of King, and as emphasized by Cross, Peale, and others, fixes the Laramie as “the uppermost member of the conformable Cretaceous series above the Fox Hills.” Being above an unconformity, the “Ceratops beds” are not a part of the “conformable Cretaceous series,” and hence can not be Laramie. This condition was correctly appreciated by Barnum Brown, who, in his paper on the “Hell Creek beds,” says: “Strictly following King’s definition of Laramie, neither of these de­ posits [“Hell Creek beds,” “Ceratops beds,” etcetera] can be considered as such, for neither one represents a continuous sedimentation from the marine Fox Hills. They should therefore be grouped with the Living­ ston, Denver, and Arapahoe beds and may be considered post-Laramie.” It was thought at one time that the ceratopian dinosaurs might be found in the same beds with the Puerco mammals, but, according to Doc­ tor Sinclair, apparently this is not so. The Puerco formation rests uncon- formably on dinosaur-bearing beds, beneath which is the “Laramie” of the region. I have shown elsewhere, however, that these latter beds are undoubtedly much older than Laramie. The “Ceratops beds,” immedi­ ately beneath those containing the Puerco fauna, have been practically traced into the Animas formation, which Cross holds is of Denver age. The Animas formation is now known to extend eastward to the eastern border of the San Juan basin, near Dulce, New Mexico, where it is con­ glomeratic at the base and consists of an andesitic matrix, in which are pebbles of many kinds of older rocks; above this conglomerate are Eocene leaves.

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I nvertebrate E v i d e n c e 6

In ninety-nine one-hundredths of the area over which the dinosaur- bearing beds are distributed there are either no invertebrates at all or they are fresh-water forms, which are generally recognized as of little value in fixing age. Marine invertebrates have come into this discussion from limited areas in North and South Dakota, where it is claimed they have been found in or above the Lance. In North Dakota from the Cannonball River northeast to Heart River, a distance of perhaps 75 miles, is a long, narrow, somewhat irregular area of sandy shales and sandstones from 200 to 300 feet in thickness which contains a considerable marine fauna. This has been called the Cannon­ ball marine member of the Lance formation. Its proposers, Messrs. Win­ chester, Hares, and Lloyd, of the United States Geological Survey, de­ fined its top as the highest point at which marine invertebrates have been found, and its base as the highest point at which dinosaurs occur. It was regarded by its proposers as a lens in the Lance formation, and is con­ sidered in whole or in part as the marine equivalent of a non-marine, coal-bearing horizon to which the name Ludlow lignitic member of the Lance has been given. Three possible explanations have been advanced by different geologists to account for the presence of this Cannonball member: (1) That it is a lens in the Lance, in which case it must have resulted from a temporary invasion of the sea after the inauguration of Eocene time; (2) that it is an erosion remnant of Fox Hills, surrounded by and projecting through the Lance, or (3) that Fox Hills time continued through Lance to Cannonball time. The first of the alternative explanations—that the Cannonball is above or a lens in the Lance—was the one adopted by the original namers of the member, is still entertained by them, and has been accepted by the United States Geological Survey.7 This means that the Cannonball is separated from the Fox Hills'by 400 feet or more of Lance beds—that is to say, that marine conditions similar to those of the Fox Hills were re­ stored for the short interval of Cannonball time after the deposition of the fresh-water Lance beds. It has in its favor the following points: (1) Its position is above the Lance; (2) it is not known to be structurally connected with the Fox Hills; (3) its fauna, though differing some­ what, is apparently most closely related to that of the Fox Hills; (4) it

6 See Knowlton, Proc. Wash. Acad. Sci., vol. 11, 1909, pp. 226-228. 7 Lloyd: The Cannonball River Lignite field, North Dakota. Bull. 541G, TJ. S. Geol. Survey, 1914, pp. 1-51.

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may be a recurrent fauna surviving from the Pox Hills fauna, which is itself partially recurrent from the Claggett (lower Montana). But this explanation requires a connection with the sea, presumably after the in­ auguration of Eocene time.

Conclusions

The thesis of this paper, as stated at the beginning, is that the line between Cretaceous and Tertiary in the Eocky Mountain region is to be drawn at the base of the dinosaur-bearing and equivalent beds—that is, at the base of the Lance, “Ceratops beds,” “Hell Creek beds,” “Somber beds,” Arapahoe, Dawson, Eaton, and “Laramie” of many writers. Evi­ dence, believed to be competent, has been presented in support of this view from the side of stratigraphy, diastrophism, and paleobotany, and what is thought to be the weakness and insufficiency of the vertebrate and invertebrate evidence has been pointed out. The vertebrate paleontolo­ gist would place the Cretaceous-Tertiary line at the highest horizon at which dinosaurs are found, notwithstanding the fact that this is a vari­ able boundary unattended by structural or diastrophic action. The in­ vertebrate paleontologist would place this line at the highest point where marine invertebrates of Cannonball types occur. The paleobotanist would place the line at the lowest horizon at which Tertiary plants have been found which corresponds with the structure. The paleontologists are not in accord. It is unlikely that they will ever be in complete agreement. What, then, is to be the court of final appeal ? There is but one answer: Structure resulting from diastrophism. The evidence from these sources supports the thesis. Why, then, shall we not be logical and rational, and agree to place the line where nature plainly indicated it rather than at some shifting, vague, and indefinite point simply to maintain a tradition?

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