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GEOLOGY OF THE SIERRA NEVADA. 47 
direction. In some localities, however, the mica schists and quartzites are 
interlaminated with each other close up to the granite. Along the Merced 
River this belt of rock is very wide; but it narrows towards the northwest. 
East of Sonora there is a large area of granite enclosed in the mica slates, 
occupying most of the space between the Tuolumne and the South Fork of 
the Stanislaus. It is this to which the mining district about Soulsbyville 
belongs. There is a much smaller insulated area of granite at Big Oak 
Flat. 
In this belt of mica schists and quartzites are found interstratified belis of 
metamorphic limestone, or saccharoidal marble, belonging to the limestone 
series mentioned before. On the Merced River there are two bands of this 
marble, one of which is almost in contact with the granite; the other at 
about three miles from it. Neither of these has been traced more than a 
few miles to the northwest, and the range of this rock seems to be broken 
until just before reaching the Tuolumne River. Here, almost in contact with 
the granitic mass mentioned before as occurring in the vicinity of Soulsby- 
ville, there is an outcrop of limestone which extends along in a curved line, 
and before reaching the Stanislaus widens out, so as to form a belt between 
one and two miles wide where it crosses that river. In the vicinity of 
Sonora, this rock is cut through by numerous dykes of diorite. 
The region of which the lithological characteristics of the bed-rock series 
have just been sketched is, in general, quite bare of overlying gravels and 
voleanic materials. Just at its northwestern border, however, and before 
reaching the Stanislaus River, we meet with the lava-flow known as the 
Sonora Table Mountain, to be described farther on. There is also another 
flow which comes down from above, and branches out in various ramifica- 
tions over the granitic mass mentioned as occurring in the Soulsbyville 
district. After crossing the Stanislaus, we find in following the auriferous 
belt along the flanks of the Sierra to the northwest, that volcanic materials, 
in the form of continuous flows, or in that of isolated patches, become more 
and_more frequent, and that these and the associated gravels cover more 
and more of the bed-rock surface, the mining localities at the same time 
becoming more numerous and important. It is not necessary or possible at 
the present time, to go into any minute description of the bed-rock in this 
region. Some general statements may, however, be made in regard to the 
order of succession of the different groups of rocks, in the auriferous belt 
north of the Stanislaus. In Mr. Goodyear’s notes on the Volcanic and 
