104 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
generally are, when found resting immediately upon the bed-rock, or at no great distance from it, 
The course of this ridge is northeast and southwest, and a line of detached hills of similar character 
extends for several miles to the southwest, appearing to cross the railroad a mile or more below 
Colfax. 
On the south of Forney’s, on Pilot Creek, the country around, within a radius of two or three 
miles, spreads out into a broad, gently-undulating tract, where the gulches are shallow, and most of 
which seems to drain towards Pilot Creek, although its general surface is not very far from level. 
This whole area, so far as could be seen, is covered with voleanic cement. At a point not far from 
two miles, in a direction 8. 75° E. (magnetic) from Forney’s, is a high timbered peak, the summit 
of which is about 800 feet higher than the level of Forney’s. The volcanic cement extends to the 
foot of this peak and a very short distance up its flank. But the top and the upper 300 or 400 
feet are of bed-rock, which is here a quartzite, more or less stained with iron, and containing 
occasionally little seams of quartz. The law which generally holds good, in the region to the 
north, in the basin of the Middle Fork of the American, — that the highest crests are all capped 
with volcanic matter, — seems to be here reversed, the more elevated ridges being of bed-rock, and 
the volcanic deposits not extending above a certain zone. From this it appears probable that the 
present depth of the voleanic matter in the central portions of the broader crests in the basin of 
the Middle Fork is a fair indication of its maximum depth in the past, and that it has never 
been much deeper there than it now is. In that case, it cum never have extended much farther 
up the sides of the highest projecting peaks of bed-rock than it now does ;. or, at least, these peaks 
have never been covered by it. 
Along Hangtown Hill and Cedar Hill, near Placerville, the whole crest of the ridge consists of 
“black lava,” i. e., voleanic breccia, the thickness of which in places is perhaps a hundred feet, 
and which contains many fragments or boulders of enormous size, some weighing from fifteen to 
twenty tons. Many of these are very angular and unworn, although they are generally somewhat 
more rounded on the corners than is usually the case with the boulders seen on the surface of lava 
streams. This breccia is underlain by smoothly washed voleanic gravel, here known as “ moun- 
tain gravel,” and under this again is the ordinary metamorphic auriferous gravel. 
In the Franklin Claim on the south side of Little Spanish Hill, as well as at Negro Hill, near 
Placerville and elsewhere, the “‘ black lava” or voleanic breccia is traversed by horizontal planes of 
stratification, proving the occurrence of successive flows of brecciated matter over the same ground. 
In the Franklin Claim the lowest stratum of “black lava” is four or five feet thick. Above it is 
a layer of sand and fine gravel a foot to eighteen inches thick, said to contain some fine gold, and 
over this again are several successive layers of “black lava.” Along the southern side of Little 
Spanish Hill the gravel is generally immediately overlain by “black lava.” There is no “ moun- 
tain gravel” in this hill. 
At Smith’s Flat, about three miles east of Placerville, the “white lava” occupies most of the 
surface. The bed ranges from twenty to thirty feet or more in thickness. The gravel beneath it 
is worked by inclines. At thirty feet below the bottom of the white lava, the gravel still contains 
boulders of this rock intermingled with the other materials. These boulders must have come from 
some considerably older deposit of the same kind of rock higher up in the mountains. 
Near the Toll House, about one and a half miles N. 8° E. from the Try Again Tunnel, there is 
a high bluff of the “white lava,” in which rude columnar forms are well developed; the top of 
this bluff is not less than 200 feet above the Toll House, and the bed-rock at the house is buried 
beneath some sixty feet of the same material. In the hill back of the face of the bluff, therefore, 
there cannot be less than 250 feet in thickness of this material. It is overlain, on the narrow crest. 
of the spur immediately east of Smith’s Flat, by a shallow bed about half-way in character be- 
tween the “black lava” and the “mountain gravel.” The “white lava” here contains a good 
many small cavities filled with a substance which has much resemblance to little fragments of 
fossilized wood. The material does not show in its internal structure, at this point, any distinctly 
horizontal bedding ; but the weathered faces of the columns indicate it by a corrugation of their 
