CORRELATION OF SUNDANCE AND MORRISON 263 



Until 1905 the Morrison was held to be overlain by the Dakota, the 

 basal deposit of the great Cretaceous invasion. In that year, however, 

 Lee and Stanton found that the Comanchian seas overlapping fi^m the 

 Gulf of Mexico northward into Kansas and Colorado spread over the 

 Morrison in Washita time, and that the latter in turn was overlain by 

 the Cretaceous (Coloradoan series). This relation, Stanton writes,^^ 



"was seen on Purgatoire River south of La Junta, Colorado ; on the Cimarron 

 from Garrett, Oklahoma, to the neighborhood of Folsom, New Mexico ; on the 

 Canadian north of Tucumcari, New Mexico ; and finally in Garden Park, near 

 Canyon City, Colorado, at the noted locality for Morrison vertebrates." 



In parts of Wyoming the Morrison is disconformably overlain by the 

 Cloverly, also regarded as of Comanchian age, for it lies beneath the 

 Benton shales of undoubted Cretaceous time, there being no Dakota sand- 

 stone here. 



Finall}', Lee^* regards the Morrison as not only of Lower Cretaceous 

 time, but even as "late Lower Cretaceous." He comes to this correlation 

 because of what he regards as the intimate stratigraphic relation of the 

 Morrison to the higher Purgatoire formation and the paleophysiography 

 of the time of its origin. 



Conclusions. — From the evidence presented, it is clear to the writer 

 that the fresh-water Morrison deposits not only overlie the marine Sun- 

 dance, but that the former is a transgressing formation and is separated 

 from the latter by a time break or disconformity. How long this erosion 

 interval lasted is not yet ascertainable from the physical evidence, nor 

 will the fossils directly answer this question, because they are rinlike cri- 

 teria, since those of the Sundance are of a marine habitat, v^hile those of 

 the Morrison are of the land. However, the fossils of the Sundance indi- 

 cate clearly that they are not at all of the latest Jurassic, but rather that 

 enough time was left in this period for the deposition of the Morrison. 

 Against the conclusion that the Morrison is of Jurassic age are the views 

 of the paleobotanists and those of the American vertebrate paleontolo- 

 gists. On the other hand, if we depend wholly on the correlations of the 

 Germans regarding the Tendaguru succession, then the Morrison appears 

 to straddle the interval between the Upper Jurassic and the Lower Cre- 

 taceous. That we are not obliged to accept this view is borne out by the 

 suggestion of Buckman (see page 278), who would refer the Upper Dino- 

 saur zone of the Tendaguru also to the Jurassic, because it is intimately 

 connected with the Trigonia smeei zone of late Kimmeridgian time. 



23 rp^ y^^ Stanton : The Morrison formation and its relation with the Comanche series 

 and the Dakota formation. Science, new ser., vol. 22, 1905, p, 756. 



24 Op. cit., p. 305. 



