94 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
ness ; it thins out rapidly in going up on the rim to the west, and also in the opposite direction 
towards the deeper portion of the channel, which has not been worked so as to expose the rim- 
rock on that side. The gravel is chiefly made up of boulders of metamorphic rock, which are 
remarkably uniform in size, few of them being over 100 or 150 pounds in weight. Immediately 
over this gravel lies a heavy mass of the material called “gray cement” of Deadwood. It con- 
tains occasional large and hard boulders of volcanic material, and many small ones. 
At the Paragon Mine, at Bath, or Sarahsville, near Forest Hill, a tunnel has been run first 
2,200 feet N. 464° W., then 1,250 feet N. 38° W., then 400 feet N. 7° W., all magnetic, making 
3,850 feet in all, to a point in the gray mottled volcanic cement which here cuts off the gravel as 
elsewhere described. It is entirely in the gravel, except the last 100 feet, which is in the volcanic 
cement, and the distance down to the bed-rock is not accurately known, although it is probably 
between 75 and 100 feet. In this mine they are following a “ pay-streak,’’ which extends nearly 
horizontally through the gravel and varies from one to six or seven feet, but averages about three 
feet, in thickness ; this they call the “lead,” and the men working it can distinguish its limits at top 
and bottom, although the difference between the pay-streak and the material in which it is enclosed - 
is so slight that it is hardly perceptible to one not trained to observe it. The “lead” appears to 
be a little less sandy, and of a rather more reddish color, and harder than the gravel above and 
below it. This gravel is made up chiefly of pebbles and boulders of hard metamorphic rock, with 
but little quartz and no perceptible volcanic rock. Below the “lead” is what the miners call 
“blue gravel”’; it is grayish in color, and has somewhat more of a bluish tinge than the “lead” 
itself. Immediately above the paying stratum there is usually more or less gravel, the boulders 
and pebbles of which are perfectly similar to those of the “lead” ; but whose finer portions con- 
sist of a gray granitic-looking sand, with much mica, and which appears to be of volcanic origin. 
Above this comes a heavy mass of what is now a soft rock, made up of a consolidated mottled gray 
and white sand, precisely like that in the gravel above the “lead,” and containing much mica, in 
scales, and quartz in grains. This material is unquestionably a bed of volcanic ash, and belongs to 
the class of the so-called “ white lavas’? so common around Placerville and elsewhere ; though its 
whole appearance is strongly suggestive of a granitic sand which has become consolidated and then 
partially decomposed, especially as it also has mixed with it considerable clay, apparently the result 
of the decomposition of feldspathic material. A vertical air-shaft was raised in this mine to the sur- 
face, and this furnished the following section. First 27 feet of gravel, including the ‘‘lead” ; then 
107 feet of the above-described gray volcanic sandy material; then 7 feet of quartz gravel, and 
above this to the surface the ordinary bouldery volcanic cement, 274 feet in thickness. The aver- 
age breadth of the strip worked out in this mine is between 200 and 300 feet, and the “lead” has 
for a distance of 2,200 feet from the mouth of the tunnel a gently descending slope to the north- 
west. But at this point the grade changes, and from thence in to the end of the tunnel the 
“lead” has a gently ascending grade towards the northwest ; in the drifts running northeast from 
the tunnel, however, there is always an ascending grade. In fact the form of this stratum is pre- 
cisely that of a very wide and shallow V-shaped trough whose breadth is some 4,000 feet, and 
whose axis, running northeast and southwest, has a gently descending grade towards the south- 
west. 
In the New Jersey Mine, at Forest Hill, the gravel on the bed-rock is generally but a few feet 
in thickness, varying from nothing up to seven or eight feet. The pebbles are very largely, 
although not exclusively, quartzose ; those which are not quartz are of metamorphic rock, and 
there are none of volcanic origin. Immediately above this gravel there is, over large areas in the 
mine, a layer, varying from an inch to a foot or more in thickness, of a rather hard and pure white 
clayey material, containing some gritty particles. Over this again comes a heavy stratum of so- 
called “ cement,” which is of a very light granite-gray color, somewhat sandy, full of scales of mica, 
and containing some clayey matter. This cement is very similar to that which overlies the gravel 
at the Paragon Mine, but somewhat harder and generally of rather finer texture than that. In 
many places on the higher bed-rock this cement closes down on to the rock itself, the gravel being 
