September 6, 1889.] 



SCIENCE. 



163 



Mr. Scudder has referred the insect remains to the tertiary, but 

 the vertebrate remains, especially those of mammals and land rep- 

 tiles, are of more ancient types than those of the plants and inver- 

 tebrates. Among the few Laramie mammals that have been 

 discovered there is no indication as to the ancestry of that great 

 mammalian fauna which characterized the immediately following 

 Wasatch period. The reptiles are mainly dinosaurs of cretaceous 

 types, but some of them seem to possess characters that suggest 

 their Jurassic age. 



Some paleontologists have long hesitated to give an opinion as to 

 the true taxonomic position of the Laramie formation ; but those 

 who have studied the vertebrates only have usually referred it un- 

 qualifiedly to the cretaceous, apparently assuming that, containing 

 dinosaurian remains, it could not be of later age. Field geologists, 

 especially those who practically ignore paleontological evidence, 

 also refer the Laramie to the cretaceous, because of its intimate 

 stratigraphical relation to the marine cretaceous beneath it, and be- 

 cause in all the principal displacements, which the latter has suf- 

 fered in the interior region, the Laramie was equally involved. 



The formations which overlie the Laramie were, by common 

 consent, long regarded as of tertiary age; but concerning the age 

 of some of them, difference of opinion have since arisen. Between 

 the Laramie and any overlying formation there is often, but not al- 

 ways, unconformity. In Utah, and apparently in the valley of the 

 lower Yellowstone also, I have found the Laramie passing gradu- 

 ally up into purely fresh-water deposits without any stratigraphical 

 break. In the former case I am sure, and in the latter case I be- 

 lieve with Professor Newberry, that the upper strata represent the 

 lower part of the Wasatch group. 



In Utah several of the fresh-water molluscan species, which are 

 widely distributed in the Laramie, are found to have passed up into 

 the Wasatch, thus confirming the stratigraphical evidence of the 

 immediate succession of the Wasatch upon the Laramie. In 

 southern Wyoming dinosaurian remains are found in some of the 

 uppermost strata of the Laramie ; and the lowermost Wasatch 

 strata in the same region bear coryphodont and other placental 

 mammalian remains ; but remains of these two orders have never 

 ■ been found commingled. Still, in view of the facts just stated, it 

 is not possible to doubt that those placental mammals lived con- 

 temporaneously with at least the last of the Laramie dinosaurs. 



In north-western New Mexico and south-western Colorado, Pro- 

 fessor Cope has found certain strata at the base of the Wasatch, 

 and overlying the Laramie, to contain the remains of a peculiar 

 vertebrate fauna whose distinguishing members are placental mam- 

 mals which are quite different from those of the Wasatch. These 

 strata he designates as the Puerco group, and he now refers them, 

 together with the Laramie, to the cretaceous, because of certain 

 characteristics which the Puerco mammalian and reptilian remains 

 present ; but he formerly regarded that group of strata as of Ceno- 

 zoic age. These Puerco strata have the appearance of having been 

 deposited simultaneously with those which elsewhere constitute the 

 lower portion of the Wasatch group ; and before their vertebrates 

 were studied by Professor Cope their identity with the Wasatch 

 was not questioned. 



But we are not yet done with dinosaurs. Mr. George H. Eld- 

 ridge has lately shown that in the vicinity of Denver, Col., there is 

 a distinct formation, from 600 to 1200 feet in thickness resting un- 

 conformably upon the Laramie, which he has called the Arapahoe 

 formation. Mr. Whitman Cross has also lately shown that still 

 another formation in the same district, having a maximum thick- 

 ness of fourteen hundred feet, rests unconformably upon both the 

 Arapahoe and Laramie formations. To these strata he has given 

 the name of Denver formation. The great aggregate thickness of 

 these formations, together with their respective displacement with 

 relation to the Laramie and_to each other, shows that much time 

 must have elapsed between the deposition of the uppermost Lara- 

 mie strata in that district and the uppermost Denver strata. 



Mr. Cross shows that a large part of the plant remains, which 

 have been reported as coming from the Laramie in this district, 

 really came from the Denver formation. Some of the fresh-water 

 mollusca of the Denver strata I am not able to distinguish from 

 Laramie species. But the most unexpected fact of all which these 

 gentlemen have brought out is that both these formations above 



the Laramie contain dinosaurian remains in comparative abun- 

 dance. The skull in some species is found to bear a pair of horns 

 similar in posture and shape to those of the hollow-horned rumi- 

 nants. Some of the bones also present characters which are sug- 

 gestive of earlier mesozoic age ; but in a general way, at least, 

 these dinosaurs are similar to those of the Laramie. 



The Laramie group does not reach its maximum thickness in the 

 Denver district, and it is not known whether the latest Laramie 

 strata are represented there. Both the Denver and Arapahoe for- 

 mations are of limited extent, and it is quite probable that the lat- 

 ter, and perhaps the former, together represent the later portion of 

 the Laramie period. But it is reasonable to infer that at least the 

 later portion of the Denver formation was contemporaneous with 

 the earlier fresh-water eocene strata of the Green River basin, not- 

 withstanding the fact that the former bears dinosaurian remains. 



The present state of our knowledge seems to justify us in regard- 

 ing the marine cretaceous formations immediately beneath the Lar- 

 amie as representing the Senonian of Europe, perhaps including 

 even a part of the Danian. Now if we add to the American creta- 

 ceous the Laramie, Arapahoe, and Denver formations, we evi- 

 dently extend the cretaceous in America much beyond its recognized 

 latest limit in Europe. 



But why, we may ask, should not those dinosaurs have survived 

 from mezozoic, into tertiary time ? Why should they not have con- 

 tinued their existence as long as physical conditions were favora- 

 ble, and as long as they could compete in the struggle for existence 

 with such mammalian faunas as that whose earliest known history 

 is recorded in the earlier strata of the Wasatch formation ? 



Before summarizing the conditions of the mesozoic of the inte- 

 rior region and proceeding to a consideration of the Pacific coast 

 section, I wish to refer to the relation of the Lamarie group with 

 the marine tertiary of the Gulf and the Atlantic coasts. 



For reasons presently to be mentioned, no direct stratigraphical 

 proof of contemporaneity of our great fresh-water inland deposits 

 with marine coast deposits is possible, and direct paleontological 

 proof is not to be expected. I had long hoped, however, that be- 

 cause the Laramie group was in part of brackish water origin its 

 continuity or contact with some marine coast deposit might be dis- 

 covered. Such a discovery was first announced by Professor Cope, 

 which I afterward confirmed, and showed that in the vicinity of 

 Laredo, Texas, the Laramie group as a whole underlies with appar- 

 ent conformity marine strata which contain an abundance of Car- 

 dita planzcosta and other characteristic eocene fossils ; but I was 

 not able to detect the continuity of the Laramie with any sea-coast 

 formation. 



It was this discovered relation of the Laramie to the Gulf coast 

 eocene that was referred to by the suggestion in a previous para- 

 graph that there is really an important hiatus, although apparent 

 conformity, between the cretaceous and the tertiary deposits of the 

 Atlantic coast. The Gulf coast eocene just mentioned being re- 

 garded as equivalent with that of the Atlantic coast, and the up- 

 permost marine cretaceous immediately beneath the Laramie, as 

 equivalent with the uppermost marine cretaceous of the Atlantic 

 coast, it follows that the hiatus referred to equals the whole of the 

 Laramie. It may also be mentioned in passing, that, both upon 

 stratigraphical and paleontological evidence, I regard both the 

 northern lignitic of Hilgard in Mississippi and its equivalent in 

 eastern Texas as equivalent with the upper, lignite-bearing, por- 

 tion of the Laramie as it occurs in the valley of the Rio Grande. 



Very briefly summarizing the mesozoic of the interior region, we 

 find that its lower delimitation is greatly lacking in uniformity, the 

 lowest member being sometimes the triassic, sometimes, but 

 rarely, the Jurassic, and sometimes the cretaceous. The triassic 

 apparently represents the upper trias of Europe, the Jurassic, the 

 upper Jura, and most of the cretaceous, the upper part of that sub- 

 division of the mesozoic. Above the marine cretaceous strata, in- 

 land sea and lacustrine deposits were continued into tertiary time, 

 apparently without a break, either paleontological or stratigraphi- 

 cal. 



Having to deal with extensive inland deposits alone when inves- 

 tigating the immediate relation of the mesozoic to the cenozoic in 

 the interior region, we find that the most direct means of deter- 

 mining such relationship is wanting, because the continuity of the 



