300 



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RESUME AND THEORETICAL DISCUSSION. 







wandering miner. The position of the large, nearly isolated patches of 

 gravel which occur in the Coast Ranges it seems not easy to account for. 

 The probability is strong, however, that the localities where such masses 

 exist were situated at the mouths of large streams, which drained consider- 

 able areas of the land forming the uplifted masses along the edge of the 

 ocean. The material which is accumulated near Sunol Valley, for instance, 

 must almost certainly have been brought down by fluviatile agencies from 

 the great area of metamorphic rocks lying to the south, where the Monte 

 Diable Kange is from thirty to forty miles in width. That these Coast Range 

 gravels are not sufficiently auriferous to pay for working, it is not difficult 

 to understand. The rocks themselves, out of which this detritus was formed, 

 have not been mineralized in their present position. They may have come 

 originally from the Sierra Nevada, which, as it seems reasonable to believe, 

 was the source of much the larger portion of the material out of which the 

 Coast Ranges have been built. But it is not certain that the impregnation 

 of the Sierra rocks with gold had already taken place at the time when the 

 Coast Range material was eroded from them ; and this is a point which will 

 be discussed somewhat further on. If, however, such impregnation had al- 

 ready occurred before the beginning of this erosion, it is still altogether prob- 

 able that much the larger part of the gold which the abraded material might 

 have contained would have been deposited before it had reached an area so 

 distant from the place from which it started. Be this as it may, it is certain 

 that the Coast Range formations have not been independently mineralized 

 with the precious metals since their deposition. They arc destitute of pro- 

 ductive quartz veins, and contain among the valuable ores of the metals only 

 those of quicksilver in sufficient quantity to pay for working. 



The distribution of the detrital formations in the Sierra Nevada is well 

 indicated by the character and extent of the mining operations, which are at 

 the present time, or have been formerly carried on. The geological struc- 

 ture, the topography, and the climatalogical peculiarities of different parts of 

 the State are all reflected in the development of the mining interests. 



In order to apprehend clearly the distribution of the detrital formations 

 along the western slope of the Sierra, the nature of the different kinds of 

 mining operations in use in California must be borne in mind, and may again 

 be briefly noticed.! We have to distinguish, first : river, bar and gulch mining, 



* Chromic iron is also considerably abundant in the Coast Range rocks, and may at some future time be worked 

 with profit. 



t See ante, pp. 65, 66, and 74-78. ' 



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