136 



THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 



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and the volcanic. The vertical thickness of the sandstone on the top of the 



outer edge of the rim-rock is somewhat over forty feet. The tunnel was run 



1,000 feet before the channel was struck, and the rim-rock rises 142 feet 



above its floor. The channel is 100 feet wide at this point, and in it there 



is a sharp projecting ridge of slate three feet high, the gravel being four 



or five feet thick. Work was begun in this tunnel in October, 1855, and the 



pay dirt struck in March, 1860. The cost of the work, up to the time of 



striking the channel, had been about $38,000, according to the statements 

 of the owners. 



Still farther down, nearly opposite Jamestown, Mr. Reraond made another 

 section at the Eureka Tunnel, which is here appended (Plate E, Fig. 2). The 

 rim-rock eroded away the northwest side, so that the tunnel is run in on the 

 gravel, the channel appearing here to be very wide. The basalt capping is 

 about sixty feet thick, and 700 feet wide. The underlying sedimentary 

 material consists of bluish soft sandstone, resting on whitish clays, the whole 

 stratified deposit having a thickness of about eighty feet, while the undei 

 lying gravel is only two feet thick. 



According to information obtained from the miners, the channel under 

 Table Mountain is of irregular width, sometimes dividing into two parts, but 

 averaging perhaps sixty or seventy feet. The gravel is shallow, and the 

 rim-rock exceedingly well marked, when not eroded off on one side or the 

 other. The course of the channel is also very easily distinguished, since 

 the flow is so isolated in its position. The main channel is said to have occa- 

 sional depressions, or " sinks," as they are termed, which are sometimes as 

 much as forty feet deep. The gold is pretty coarse, usually in the form of 

 what is called " shot gold " • that is, in small rounded pieces like shot. The 

 largest nugget the writer heard of as having been found under Table Moun- 

 tain was of $ 40 in value. 



The large quantity of silicified wood and of impressions of leaves found in 

 the sedimentary beds under Table Mountain has already been noticed. Bones 

 of animals and works of men's hands are also among the materials obtained 

 in the tunnels which have been described or in other workings under the 

 lava. These will be noticed at length in a future chapter of this volume. 



When Table Mountain was last visited by the writer, in' 1870, all the above- 

 described tunnels seemed to be entirely abandoned. That mining operations 

 lower down on the channel were not quite given up seems apparent from 

 Mr. Skidmore's remarks in his report to the United States Commissioner of 





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