COKRELATION OF SUNDANCE AND MORRISON 261 



[underlying aud overlying] marine faunas serves to fix definitely the time 

 limits within which the Morrison must fall." 



"The Morrison must be older than Cenomanian and probably younger than 

 Oxfordian. That it represents all of this interval is not probable. ... So 

 far as stratigraphy and invertebrate faunas are concerned, the Morrison is 

 somewhat more likely to belong to the Jurassic portion of the interval just 

 indicated than to the Cretaceous portion; but their evidence is not conclusive 

 on this point." 



Evidence of the dinosaurs. — In his study of the Maryland Lower Poto- 

 mac (Arundel formation) reptiles, LulP^ says that they 



"compare very closely" with those of the Morrison, "and, in some instances, 

 very closely allied if not identical species are found in the West. A striking 

 similarity also prevails between the Potomac on the one hand and the Wealden 

 of Europe on the other." Further, the Arundel formation correlates "abso- 

 lutely with the Morrison of the West. . . . The weight of this evidence 

 would seem to place this fauna beyond the Jurassic into the beginning of 

 Cretaceous times." 



To these statements should be added that now all of the Potomac is re- 

 garded as of post-Jurassic age and in the main Comanchian. In a latei' 

 paper, however, LulP^ modifies his conclusions as follows : 



"Correlation based on the sauropod evidence between Europe and America is 

 not to be relied on at present, but we can evidently point to the middle [and 

 the upper dinosaur] Tendaguru horizon of East Africa, which contains the 

 genus common to the Morrison, as homotaxial with the latter." 



Osborn^^ states that among the carnivorous and the large herbivorous 

 dinosaurs there are 



"forms resembling those which range from the Oxfordian through the Kim- 

 meridgian into the Purbeckian and even into the Wealden. In general, it is 

 said the Morrison dinosaurs are more specialized than those which have been 

 found in the true British Jurassic formations, but there are some very striking 

 exceptions. . . . All the camptosaurs of the Morrison are more generalized 

 and primitive in structure than the iguanodonts of the Wealden. . . . The 

 mammals appear to be closely related in their stage of evolution with those of 

 the Purbeckian of England. . . . Geologically the stratigraphic relations 

 certainly appear to favor Lower Cretaceous, or Comanchian, age for large por- 

 tions of the Morrison." 



Correlations. — As long as the Morrison was held to be intimately united 

 with the Sundance and in unbroken connection with it, it was natural to 

 regard the former as of Upper Jurassic time, and this conclusion was all 



1'^ R. S. LuU : The Reptilia of the Arundel formation. Maryland Geol. Surv., Lower 

 Cretaceous, 1911, pp. 173, 178. 

 , 18 R. S. Lull : Bull. Geol. Soc. Am., vol. 26, 1915, p. 334. 

 " Op. cit., pp. 298-301. 



