32 GEOLOGY OF THE EUKEKA DISTRICT. 



been studied they resemble closely those found in the neighboring valleys, 

 and do not offer much of special or local interest. 



During the Quaternary period vast accumulations of detrital material 

 were brought down from the mountains and transported far out upon the 

 neighboring plain or laid down upon the flanks of the outlying foothills. 

 These deposits have been classed under two distinct epochs an upper and 

 a lower Quaternary. 



Lower Quaternary. The earlier deposits, or the lower Quaternary, are 

 for the most part lacustrine, made up of finely comminuted stratified sands 

 and clays carrying varying amounts of calcareous material. All the beds 

 have a prevailing light yellowish color. - They form the so-called alkali 

 flats of Nevada, and when dry resemble a hard tile pavement, but when 

 moist have all the disagreeable qualities of a plastic clay, well nigh impas- 

 sable. Nowhere within the neighborhood of Eureka have they been cut by 

 water channels for more than a few feet, and at the time of our investigation 

 no deep borings for water had been made. In consequence no reliable data 

 exist for a correct estimate of their thickness, which in places ma}- reach 

 several hundred feet. No recent shells have as yet been found in the few 

 exposures observed along the stream beds. On the map the line of de- 

 marcation between the upper and lower divisions of the Quaternary has 

 been drawn somewhat arbitrarily, it being by no means easy to separate, 

 sharply, the finer material of the upper series from the lacustrine deposits 

 underlying them. 



Upper Quaternary. The upper or mountain Quaternary is made up of 

 angular material varying in size from large bowlders to fine sand and 

 gravel. It is in all cases traceable to the neighboring mountains, the nature 

 of the coarser fragments depending upon the rock exposure above it. The 

 material is subaerial in origin. It everywhere fringes the flanks of the 

 mountains, encroaching upon the area of the underlying lacustrine beds for 

 shorter or longer distances, according to the configuration of the hill-slopes 

 or the transporting power of floods and freshets. The finer material is, nat- 

 urally, transported the greater distance, consequently it gradually becomes 

 mingled with and forms a superficial layer over the lower Quaternary de- 

 posits. South of Prospect Peak and opposite the entrance to Secret Can- 



