136 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
and the voleanic. 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. Rémond made another 
section at the Eureka Tunnel, which is here appended (Plate HE, 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 under- 
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 
