PERSISTENCE OF TDE SIERKA NEVADA. 209 



It is hoped tliat work now being done on the goUl belt may alFord a 

 definite answer to this and other questions. In the absence of distinct 

 evidence, liowever, the probabiHties appear to be against the supposition 

 that all the metamorphism which can be traced in this State is referable to 

 a single period. 



It may be asserted with some confidence, as a result of all the geologi- 

 cal work done from the Rocky Mountains to the Pacific, that there has been 

 throughout geological time a definite tendency in the structural development 

 of this area. The geologists of the fortieth parallel exploration showed 

 that a fault began upon the west flank of the Wahsatch in the Archean, the 

 same fault which Mr. Gilbert has traced as still in progress. The last- 

 named geologist and Prof. Joseph Le Conte have also detected a similar 

 fracture on the east side of the southern portion of the Sierra. The eastern 

 portion of the Great Basin was lifted above the surface of the ocean after 

 the close of the Carboniferous, the western portion of the same area fol- 

 lowed before the Cretaceous, and at one or both of these epochs the coun- 

 try was laterally compressed, an action no doubt closely connected with 

 the progress of the great faults. About the time of the Neocomian Cal- 

 ifornia experienced an east and west compression, and again at the close of 

 the Miocene an uplift threw the horizontal strata of the coast into north and 

 south folds. From the Wahsatch to the Pacific Coast there thus appears 

 to have been a recurrent, if not a constant, tendency to lateral compression 

 in substantially one and the same direction and to an increase of the land 

 area west of the Wahsatch. 



This repetition of movements in a similar direction has tended to ob- 

 scure the time relations of geological phenomena, particularly along the 

 great Sierra Range, which has probably been one of the most persistent 

 topographical features of the continent. Dr. White points out that an ex- 

 traordinary difference has existed between the marine fauna of the Pacific 

 Coast and that of the waters east of the Sierra from a time prior to the 

 Cretaceous onward, and hence that a land barrier must throughout have 

 occupied substantially the position of the Sierra Nevada, which must there- 

 fore have experienced repeated upheavals to compensate for constant ero- 

 sion. There are also said to be some paleontological grounds for sup- 

 MON xiii 14 



