272 GEOLOGY. 
alluvium. The slates crop out along a ravine, but the top of the hill is formed of deposits, 
which reach a thickness of 200 feet or more. They rest upon a basin-like depression in the bed- 
rock, and the gold-bearing layer is at the bottom. In order to reach this, tunnels are cut in 
from the side of the hill, at such a distance below the summit that the lowest part of the basin 
will be intersected. To do this, it is necessary to cut through the outer or projecting rim of slate 
rock, and some of the tunnels are thus of great length and very costly. 
SECTION OF THE HILL-SIDE AT GEOEGETOWN. 
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The relative positions of the drift and the slates, and the method of mining, will be under- 
stood from the section. A ‘‘ prospecting ”” shaft is first sunk from the surface of the bed-rock, 
and the earth tested. If the result is favorable, a tunnel is commenced on a level with the 
bottom of the shaft, or at a lower point, and carried in so as to intersect the shaft, or so as to 
strike the ** pay-dirt’’ at a favorable point. The auriferous earth is then removed in all direc- 
tions, and sent out of the mine by cars on a tram-road, and emptied down a slope or guide of 
boards into a large bin made to receive it. From this it is taken and washed in a board-sluice. 
About two feet of the earth and gravel next the slates, and even the upper edges of the slates 
to a depth of a foot or more, are removed, and the roof is supported by timbers precisely as in & 
coal mine. The whole operation of mining is very similar to that of beds of coal, where they 
occur above the level of streams, and are nearly horizontal, as at Pittsburg and other places. 
The claim of-the Mameluke Tunnel Company is opened by a cutting of at least 300 feet in 
length through the slates before the gold-bearing earth is reached. This forms a layer not 
over two feet in thickness, and rests immediately upon the upturned edges of the slates. It is 
overlaid by a firm and homogeneous deposit of clay, which is said to be eighty feet thick and 
without coarse materials, It has a dull ash-color, and contains a large quantity of pumice or 
volcanic ashes. Some of the masses, which have been removed in the course of mining, are 
traversed by cylindrical holes, looking like the casts of vegetation or roots that have since 
decay ed and disappeared. - In one of the specimens a perfect cast of a leaf was found. Itis 
probable that this is a lacustrine deposit—the sediment from an ancient pond or lake that 
occupied a valley in the slates. What changes have been produced in the configuration of the 
surface of the region since that lake wag drained! — 
It is said that the following succession of beds was foi in sinking the shaft of the Bay State 
Tunnel Company : 
Feet. 
Surface MARIA I (soil and gravel) Me: 
Gray argillaceous beds, with volcanic ejections, pumice, &e., (** cement). .. ...... 40 
: q gravel, (** pay gravel’’) ; ; 8 
Gray with pumice, (e (cement). . oo» 60 
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