572 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Bradley mentions proof of two eruptions,* the layers of which are sep- 

 arated by sand and gravel. I am inclined to think the basalt of Station 

 81 is older than either of the layers mentioned by Professor Bradley. 

 North of Boss Fork the axis of the Bannack Bange disappears entirely 

 beneath the accumulations of Snake Biver plain. 



We have seen, therefore, that the Bannack Bange is one of the iso- 

 lated ranges so common in the region of the Great Basin, and like the 

 others is a remnant of a system of folding. The northern portion shows 

 one side of ananticlinal, while the southern portion shows the other. 

 Erosion has removed a great mass of beds, and the valleys on either side 

 are filled with later lacustrine deposits. There is no evidence, either in 

 this range or in the Portneuf Bange, of the faulting noticed by King in 

 the main Wahsatch Bange, and the absence is further proof that the 

 faulting in the latter took place after a period of complicated foldings, 

 as held by King.t I shall refer to this point again in a subsequent 

 chapter when speaking of the district as a whole. 



* Report U. S. Geol. Survey, 1872, 1873, p. 204. 

 t Exploration oftlie 40th Parallel, Vol. I, p. 735. 



