262 C. SCHUCHERT MORRISON A^'D TENDAGURU FORMATIONS 



the more legitimate, since previous to fifteen years ago European stratig- 

 rapliers were unanimous in regarding the Wealden as of the same time. 

 Xow the Wealden is regarded by all stratigraphers as of the early Tjower 

 Cretaceous^ and because of this reference and the similar nature of the 

 Morrison and Wealden faunas, some American vertebratists are holding 

 that the Morrison straddles the time from the later Upper Jurassic well 

 into the Comanchian. This view is best expressed by Osborn as follows :^° 



''It will probablj' appear as the cbief result of this symposium that the inter- 

 mediate theory is correct; that . . . the Morrison sedimentation was a 

 very comprehensive and wide-spread process ; that it began in certain localities 

 earlier than in others, namely, during Upper Jurassic times ; that it extended 

 well into Lower Cretaceous times ; that all the sediments known as Morrison 

 represent a vast period of geologic time in which sedimentation was remark- 

 ably slow, because at no point does this so-called formation . . . attain 

 any considerable thickness. The more primitive forms of Morrison life are 

 partly, at least, truly Jurassic, while the more specialized progressive maybe 

 are truly Lower Cretaceous." 



Osborn refers to this view as having been first maintained by Williston, 

 but the latter was treating of the Atlantosaurus beds, as they finally came 

 to be kno^\7i, a series of strata that embraced more than the Morrison. 

 Accordingly, in 1905, Williston-^ showed that the strata affording Hallo- 

 pus and Nanosauriis have no coiniection whatever with the Atlantosaurus 

 or Morrison formation, but that they clearly belong in the Upper Tri- 

 assic. Furtlier, that at Lander, Wyoming, in the top of the Atlantosaurus 

 beds, occur fish and reptilian remains like those in the Mentor formation 

 of Kansas, the equivalent of the Washita formation of the Upper Co- 

 manchian of Texas. In other words, that the marine Comanchian Purga- 

 toire formation of central Colorado oxteiuls as far as Lauder, Wyoming. 



Williston-- is of the further ojDinion that 



"there is no ^alid vertebrate evidence pointing to an age greater than the 

 Purbeck for the Atlantosaurus beds, and but very little for a greater age than 

 that of the Wealden." "The upper part of the Atlantosaurus beds is, it seems 

 to me, indisputably Cretaceous [now the Purgatoire of Colorado and Cloverly 

 of Wyoming] ; the lowermost part [after removing the Hallopus horizon] is 

 probably not older than the Wealden, though possibly of Purbeckian age [the 

 very top of the English Jurassic]. I therefore strongly protest against the 

 common usage of referring all the fossils from these beds to the Upper 

 Jura. . . . The only proper designation for the composite faunas included 

 in them is Jura-Cretaceous ; this assumes that the Wealden is really Jurassic," 

 but now the opinion is that the Wealden is Lower Cretaceous in age, an altera- 

 tion in favor of taking the Morrison out of the Jurassic. 



="0p. cit, p. 302. 



21 Op. cit., pp. 338-341. 



22 Op. cit., pp. 347-348. 



