67 



and the gravel beds which are also found beneath the latter, are of the same 

 character in as marked a degree as the drift beds of the surface which are im 

 posed upon them. So far as those beds have been opened there appears little or 

 no exception to the rule. 



Within the last year the older conglomerate rocks have been found to contain 

 gold, but not to that extent which would warrant mining explorations. The 

 fact, however, is sufficiently well established to require notice in this place. 



The sedimentary rocks extend eastward in the more central mining counties 

 to within twelve miles of the summit ridge of the chain. Here a few imperfect 

 fossils have been found, but none of sufficient distinctness to determine either their 

 geological position or character with any degree of certainty. It is proper to 

 state however that there are some evidences of the cretaceous, or perhaps, the 

 upper secondary rocks being found in those districts, though as yet it is a mat 

 ter of much doubt, arising from the imperfect condition of the organic remains 

 found imbedded within them. 



The following table exhibits the approximate depths of the superficial cover 

 ings of the mountain mining districts, in which that department of industry is 

 conducted. The table is intended to represent the more central line of country 

 which corresponds with the trend of the chain, and is usually found at a distance 

 (air line,) of about forty miles from the eastern border of the plains. It will 

 include in its range the towns of Forest City, Nevada, Georgetown, Volcano, 

 Mokelumne Hill, and Sonora. 



TABLE. 

 Sierra. 



Gravel drift 60 feet 



Light gray and blue clays - 15 " 



Blue clays - 15 " 



Gravel and sands - 30 " 



Clays, with lignites 18 " 



Blue clays - - - 25 " 



Clays, with leaves 8 " 



Auriferous gravel - 18 " 



Slates - 22 " 

 Primitive rocks. 



Total, - 201 feet. 

 El Dorado. 



Gravel drift 60 feet. 



Blue and brown clays - 20 " 



Cemented drift, clays, and lignites 40 



Sand clays - - 20 ' 



Clays, with leaves - 10 " 



Sandy clays and lignites - 10 " 



Coarse sand, pyritous 4 " 



Auriferous gravel - 25 " 

 Primitive rocks. 



Total, 189 feet, 



