150 ANNALS NEW YORK ACADEMY OF SCIENCES 



Tliis fauna in its general cliaracter seems to require low, or at least 

 level and aquatic, conditions. Woodworth (1894, 1), in discussing the 

 relations of peneplanation to organic evolution, states that the reptiles 

 and in particular the dinosaurs are correlated in development with the 

 growth of the peneplain. He makes the following remarks regarding the 

 reptilia : 



"Eeptilia are characteristic lowland forms. They will endure the cold 

 of high altitudes and latitudes onl}^ by falling into a state of torpidity. 

 In the development of the peneplain from the high relief of the Permian, 

 and again, at the close of the Jura-Trias, the widening out of the lowland, 

 with plains and jungles near tide-level, followed by depression of the land, 

 must have highly favored the water-loving reptilia. It is to these geo- 

 graphic circumstances, I think, that we must look for an explanation of 

 the remarkable history of this class in Mesozoic times." 



Many of the forms listed above are no doubt synonyms, but their deter- 

 mination is beyond the scope of the present paper. 



AGE OF THE MOREISOJ^ FOEMATIOI^ 



The age of the Morrison formation has been the subject of considerable 

 discussion in the past. The reports of the early surveys refer to the 

 Morrison beds as "Jurassic beds," "Lower Dakota" and other terms signi- 

 fying various ages. Cope (1877, 5; 1878, 8) described typical Morrison 

 reptiles as coming from beds of the "Dakota Epoch" in Colorado. 



Cope (1884, 1) made a faunal comparison of the Morrison and 

 Wealden formations, bnt made no definite statement as to their age or 

 correlation. Osborn (1888, 2) compared the mammals of the Morrison 

 with those of the Purbeck beds, and considered the former to be of 

 Jurassic age. Emmons, Cross and Eldridge (1896, 1) stated that from 

 the point of view of the stratigrapher the assigmnent of the IMorrison l)eds 

 to the Lower Cretaceous (Comanchean) was more desirable than assign- 

 ment to the Upper Jurassic, "not only because it accords better with the 

 sequence of sedimentation thus far disclosed in the adjoining regions of 

 Kansas and Texas, but because it places the physical break whose effects 

 are recognized over the whole continent between these two great time 

 divisions rather than in the midst of one of them." Marsh (1896, 5; 

 1896, 7) vigorously maintained the Jurassic age of the Atlantosaurus 

 Beds and correlated them with the Wealden of Europe. Scott (1897, 5) 

 in his Manual of Geology placed the Morrison or Como in the Co- 

 manchean. Ward (1900, 6) considered the evidence from the cycads 

 sufficient to place the formation in the Jurassic. Knight (1900, 2) 



