550 DESCRIPTIVE GEOLOGY. 



many cracks. There are a few flakes of black mica. This outburst of vol- 

 canic rocks occurs, like so many others in Nevada, at the end of a long 

 ridge, where the sedimentary strata come to an abrupt termination by 

 plunging suddenly downward, with the break, which is evidently a point of 

 weakness, and one of least resistance, occupied by intrusive material. From 

 this light-colored limestone were collected a number of fossils, types of Coal- 

 Measure species, nearly all identical with form^ found in the Carboniferous 

 limestone of White Pine. The following have been identified : 



Chcetetes, sp.? 



StreptorhyncJms crassus. 



Produdus semireticulatus 



Productus Prattenianus. 



Produdus costatus. 



Spirifer Bockymontanus. 



Spiriferina spinosa. 



From the southern end of the range, near Newark, in a bluish-gray 

 limestone, were found : 



Chcetetes, sp.f 

 Campophyllum, sp.? 

 Spiriferina spinosa. 



West of the Diamond Range, the Lower Quaternary plains occupy the 

 central portion of the valley in a belt 4 or 5 miles in width. During the 

 winter and early months of spring, they are usually covered by a few inches 

 of water; but in summer, with the exception of small shallow ponds at the 

 northern and lower end of the valley, they present a hard level floor like the 

 Great Desert. These Lower Quaternary deposits are strongly impregnated 

 with common salt, and, upon the evaporation of the concentrated waters at 

 the upper end of the valley, exhibit broad fields of salt incrustation, which 

 have for several years been a source of revenue to those engaged in gather- 

 ing it for the purposes of silver- extraction by amalgamation. 



As the strata upon both sides of the valley dip toward each other, it is 

 not surprising that immerous springs, both hot and cold, should be found 

 encircling the valley along the base of the limestone hills. The waters are 



