72 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. 



found in strata above this physical break, and hence I agree with him in 

 considering them Tertiary. 



In subdividing the Cenozoic or Tertiary, Professor Lesquereux has 

 attempted to draw very fine lines, dividing these beds into Eocene and Mio- 

 cene, and further subdividing each of these two groups into upper, middle, 

 and lower. In doing this he has done violence to the stratigraphy, and 

 sometimes his upper, middle, and lower cross each other; but, in a general 

 way, his Miocene is higher than his Eocene. 



All of the fossils. described by Mr. Meek which have been found above 

 this physical break, he has referred unhesitatingly to Tertiary, and all of the 

 fossils found below the physical break, he has referred, unhesitatingly with 

 some, doubtfully with others, to the Cretaceous. There is a single excep- 

 tion to this in Ostrea Wyomingensis, which is a new species; and I am sure 

 no paleontologist would insist that a new species of ostrea could be used as 

 conclusive evidence in deciding the age of a group of beds. That Mr. Meek 

 did not discover the physical break is not strange, for he did not see it. 

 When he made his exploration in this region he was in ill health, and trav- 

 eled "by rail from station to station, stopping at these places and examining 

 the nocks only in the vicinity of the stations. His health would not permit 

 him to make long excursions in the country on foot, and it was impossible 

 for him to obtain horses. He passed the physical break above mentioned 

 on a railroad car, and his sections at Hallville and Point of Rocks are not 

 connected by several hundred feet, as he states, and as I have since verified 

 by passing over the ground; and the physical break is found in the gap. 

 In like manner, on the opposite side of the Aspen Mountain uplift, he passed 



it in the cars between Point of Rocks and Green River Stations. 



* 



The conclusions reached from a study of the vertebrate paleontology 

 by Professors Leidy, Marsh, and Cope entirely harmonize with this division 

 of the Cenozoic and Mesozoic. There is a single exception to this; Pro- 

 fessor Cope described a dinosaur found near Black Buttes Station as Creta- 

 ceous. I have verified the determination of the stratigraphic horizon by 

 examining the place and finding other dinosaur bones; but this horizon is 

 above the physical break, and the evidence of the dinosaur seems to be con- 

 tradicted by the evidence furnished by many other species described by 

 Professor Cope from about the same horizon. 



