MINING. 391 
tain, it wasnecessary for them to cut tunnels through a rim of 
rock ; but now that many of the tunnels have drained away all 
the water, they are started up on the hill-side above the rock, and 
cut in sloping downward, so that the hard bed-rock is avoided, 
and in many places the tunnels made on this plan may run all 
the way through soft dirt. It is established beyond all reason- 
able doubt, that the auriferous deposit under the basalt was 
once the bed of an ancient river. Every mark indicates it. 
The wide water-worn bed, the bends, the bars, the deposits of 
gravel in eddies, the collection of coarse gold in the centre, 
the position of the large flat stones, all pointing down stream, 
the remains of fresh-water mollusks, and the beds of little 
tributary streams—all these are conclusive proof that a large 
river once ran where this mountain now stands. The pay-dirt 
is a tough clay filled with large stones, and is from a foot to 
six feet deep. In one place a claim one hundred superficial 
feet square yielded seventy-five thousand dollars. The dis- 
tance from the outside of the mountain to the pay-dirt, varies 
from six to twelve hundred feet. About ten miles east of 
Sonora is the Soulsby quartz lead, one of the richest in the 
state. 
§ 225. Mono and Mariposa—Kastward of Tuolumne, east 
of the summit of the Sierra Nevada, and within the limits of 
the Great Basin, lies the county of Mono, which contains the 
gold placers of Mono Lake and Walker River, and the silver 
lodes of Esmeralda. The placers of Walker and Mono are 
neither extensive nor rich; water is scarce; and the winters 
are so cold that mining is necessarily interrupted. The Walker 
diggings are seventy-five miles southward from Carson City, 
and.the Mono placers are twenty-five miles further in the same 
direction. The Esmeralda mines are in a nest of mountains of 
the same name, most of the ridges of which run north and 
south, and are composed of eruptive rocks, such as trap and 
basalt, with occasional greenstone and porphyry. The argen- 
tifarous region lies in a rugged part of the mountains, about 
five thousand feet above the level of the sea. The ore is alla 
