CHAPTER V. 

 DESCRIPTIVE GEOLOGY. 



In the following pages will be found a detailed description of the sed- 

 imentary rocks in the Eureka District, the order followed being for the most 

 part the same as that adopted in the chapter devoted to the general 

 geological sketch. Each orographic block is described by itself, beginning 

 with Prospect Ridge, where the oldest rocks occur, followed by the other 

 blocks according to the geological succession of strata; the only changes 

 made in the order of treatment being for the purpose of bringing out more 

 forcibly the structural relations of the individual blocks to each other. This 

 chapter necessarily contains a repetition of many facts stated in other por- 

 tions of the volume, but at the same time there is an omission of many 

 details that, if not presented elsewhere, would properly find a place here. 



The principal object of this chapter is to give a connected description 

 of the country and to place numerous details in permanent form for the 

 use of those who may wish to study the field in person, or who may desire 

 to investigate more fully the facts upon which the generalizations are based. 

 Certain portions of the country are described more fully than others, and 

 in a few instances the descriptions follow closely those given elsewhere in 

 the volume. 



PROSPECT RIDGE REGION. 



This region includes all the country lying between the Hoosac fault 

 on the east side and the Spring Valley, Prospect Mountain, and Sierra 

 faults on the west. These lines of faulting sharply outline a mountain 

 block which, in its geological structure, stands out on all sides clearly 

 defined from the adjacent country. 



99 



