38 



LARAMIE FLORA OF THE DENVER BASIN.. 



and trituberculates are unmistakably those of 

 the Lance, but the placental mammals have 

 not been found in the Lance and appear to 

 belong to the Paleocene groups of mammals," 

 while the invertebrates ~ " are suggestive of 

 Fort Union rather than earlier forms. " The 

 Edmonton formation, although containing a 

 flora, at least in the upper part, that is un- 

 doubtedly indicative of Fort Union age, was 

 concluded to be Cretaceous and older than 

 Lance on account of the presence of a plesiosaur 

 (Leurospondylus) , a marine reptile "clearly of 

 Mesozoic age, " above the plants. v Brown 

 concluded as follows: 



From the vertebrate and invertebrate remains it seems 

 very clear that these rocks are not of Fort Union age, but as 

 shown by the plants the climatic conditions of Fort Union 

 time were long foreshadowed toward the close of the 

 Cretaceous. 



The dinosaur-bearing beds beneath the 

 Puerco formation of northern New Mexico 

 were briefly described under the name Ojo 

 Alamo beds. 



, , The final conclusion of the paper was as 

 follows : 



There is no doubt that the Hell Creek beds were 

 synchronous with the Lance, and little doubt that the 

 Belly River and Ojo Alamo beds should be correlated with 

 the Judith River. The Edmonton is intermediate in age 

 between the Judith River and the Lance. 



W. D. Matthew 29 stated that the term " Paleo- 

 cene" as he used it "denotes what we have 

 been calling basal Eocene, comprising the 

 Fort Union, Puerco and Torrejon, and other 

 equivalent formations older than Wasatch 

 or typical lower Eocene." Matthew gave 

 lists of the vertebrate faunas of the Puerco, 

 Torrejon, Paskapoo, and Fort Union and made 

 comparisons between them and those of the 

 Lance and Belly River and with the Wasatch. 

 In an interpretation of the faunas he stated: 

 "The evidence of fossil vertebrates in correla- 

 tion is very valuable, provided it is interpreted 

 correctly. " The difference between two faunas 

 may be due, he said, to "lapse of time; differ- 

 ence of local environment; migration move- 

 ments representing a change in environment 

 somewhere else, not' necessarily in the region 

 concerned." With these precautions in mind 

 Matthew presented the table reproduced in 

 figure 1. 



» Evidence of the Paleocene vertebrate fauna on the Cretaceous- 

 Tertiary problem: Geol. Soc. America Bull., vol. 25, pp. 381-402, 1914. 



The correlation of the faunas here involved 

 with the European succession is of special 

 interest. It was shown that the Thanetian 

 (Cernaysian) has furnished a "small fauna of 

 mammals and reptiles, comparable in facies 

 to our Torrejon and apparently of equal age." 

 The Sparnacian and Ypresian, which include 

 the London clay, the Argiles plastique.of the 

 Paris Basin, and equivalents in Belgium and 

 elsewhere, are equivalent to our Wasatch. 

 According to Matthew, the Puerco, arbitrarily 

 correlated by Osborn with the Montian, "has 

 no certain equivalent in Europe," and he 

 stated that the "Lance is equally difficult to 

 correlate," as "there are no European forma- 

 tions of corresponding facies in the late 

 Cretaceous." 



As regards faunal migrations and diastro- 

 phism the following statements were made: 



As I read the evidence from the vertebrates it is to this 

 effect: 



1. From the Belly River to the Lance there is a con- 

 siderable lapse in time, but they represent the same 

 faunal facies and they indicate that there was no great 

 migration movement intervening, and hence no great 

 upheaval, either continental or universal. There was un- 

 doubtedly a considerable local uplift along the Rocky 

 Mountain ridges and extensive recession of the sea from 

 the plains to eastward of them. 



2. Between the Lance and the Paleocene there is a some- 

 what smaller lapse in time but a very marked change in 

 fauna; but they do not represent the same facies, and 

 while a great migration movement is probably indicated 

 by the extinction of the dinosaur phyla and incoming 

 of certain groups of placental mammals (Creodonta, Con- 

 dylarthra, etc.), its extent remains a little uncertain. 



3. Between the Paleocene and Eocene a great migration 

 movement intervenes, the progressive orders of placental 

 mammals, of turtles, and perhaps other groups appearing 

 simultaneously in Europe and North America. The lapse 

 of time between the uppermost Paleocene and lowest 

 Eocene is slight. 



If, therefore, we are to use diastrophic criteria as the 

 basis of our geologic classification, the dividing line be- 

 tween Cretaceous and Tertiary should be drawn either 

 between the Lance and the 'Paleocene or between the 

 Paleocene and Eocene. It should not be drawn between 

 Belly River and Lance. 



The following is Matthew's conclusion: 



The question to my mind shapes itself thus: Does the 

 evidence conclusively support the present classification; 

 and, if not, is it sufficiently conclusive to warrant our 

 changing it? I have indicated what I regard as the weight 

 and trend of the vertebrate evidence. Without entering 

 into any detailed criticism of the stratigraphic and paleo- 

 botany evidence, a task for which others are far more com- 

 petent, I may say that to me it appears to be inconclusive 

 because it does not allow for the characteristics of epicon- 



