262 WN. LOGAN 
shallow sea in upon the continent. A very slight increase in the 
capacity of the ocean basin would suffice to draw the water off 
the continent at the close of the period. The increase in the 
capacity of the ocean may have been accomplished by a slight 
settling of the oceanic segment. The withdrawal of the waters 
of the epicontinental sea was doubtless the initial step in the 
movement which ended in the elevation of the Sierra Nevada 
Mountains ; for the withdrawal took place at the close of the 
Oxfordian stage or during the Corallian and according to Diller’ 
the orogenic movement which produced the Sierra Nevada and 
Klamath Mountains took place at the close of the Corallian. If 
these interpretations be logical ones we may assume that. it 
required little or no bodily movement of the continent to pro- 
duced either the inauguration of the Jurassic sea or its withdrawal 
from the continent. It may be asserted further that there is 
nothing connected with its history which is inimical to the doc- 
trine that the continent had in general its present outline during 
Jurassic times and that the waters of the submerged portions 
were of an epicontinental nature. 
‘The writer’s study of the faunal conditions in the field has 
led him to the opinion that only one fauna is to be recognized 
in the Jurassic deposits of the interior province. A comparison 
of the fossils collected from the different areas just discussed 
serves to strengthen the opinion. Everywhere the formation is 
characterized by about the same group of fossils, of which the 
more characteristic ones are: Lentacrinus astericus, Belemnites 
densus, Camptonectes bellistriatus, Pseudomonotis curta and Cardi- 
oceras cordtforme. These forms all existed contemporaneously. 
Stanton? discusses the view expressed by Hyatt3 that more 
than one Jurassic fauna may be represented in the Interior and 
arrived at the following conclusion: ‘‘the stratigraphic relations 
and the geographic distribution of the marine Jurassic of the 
Rocky Mountain region are in favor of the idea that all of these 
deposits were made contemporaneously in a single sea.” 
™ Bull. Geol. Soc. Am. Vol. IV, p. 228. 
2U.S. Geol. Surv. Yellowstone Park Monograph XXXII, 1899, pp. 602-604. 
3 Bull. Geol. Soc. Am. Vol. III, 1892, pp. 409-410. 
