46 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
mentioned, it occurs in detached portions, all of which, however, are nearly 
in one line, the direction of which is that of the trend of the formations 
making up the bed-rock series. In the region between the Merced and the 
Stanislaus, the Great Quartz Vein is almost continuous; it runs uninter- 
ruptedly between French Gulch and the main branch of Mocecassin Creek, 
forming by its outcrop in the Pejia Blanca a very conspicuous object, and 
having there a width of 261 feet, measured horizontally across it, its melina- 
tion being to the northeast at an angle of about 60°. Beyond Moccassin 
Creek it disappears for a time, but is seen again below Stevens’s Bar, on the 
Tuolumne, and at numerous points between there and the Stanislaus. This 
powerful lode is made up of irregularly parallel plates of white compact 
quartz, and crystalline dolomite or magnesite,* more or less mixed with 
green tale; and these plates, which somewhat resemble the “combs” of ordi- 
nary lodes, are either in contact or separated from each other by intercalated 
layers of talcose slate. The quartz is chiefly developed in the central portion 
of the vein; and, from its color and resistance to decomposition, it gives rise 
to a very conspicuous outcrop, forming the crest of the hills, so that it can be 
readily seen from a distance of several miles. The dolomitic or magnesitic 
portion decomposes somewhat readily, and it becomes a kind of “ gossan,” 
or a cellular, ferruginous mass, of a dark-brown color, often traversed in every 
direction by seams of white quartz. The quartz is the auriferous portion of 
the lode, although it is far from being uniformly impregnated with gold. 
Most of the mines which have been worked, between the Merced and the 
Stanislaus, are on the northeast side of the Great Quartz Vein, either in con- 
tact with it, or in some parallel band of quartz subordinate to, or at a little 
distance from it. The talcose slate bands in the vein are often, themselves, 
more or less auriferous. 
Beyond the belt of metamorphic volcanic rock, which lies to the northeast 
of the band of argillite and serpentine just described as containing the Great 
Quartz Vein, there is a wide belt of mica slate, which extends to the gran- 
itic nucleus of the Sierra. This is, in the region between the Merced and 
the Stanislaus, the second great series of metamorphic schists belonging to 
the bed-rock system. These mica schists are more or less quartzose on the 
southwest, and they pass into pure quartzites as we approach the granite, 
the proportion of argillaceous material in them gradually diminishing in that 
In the only specimen which has thus far been chemically examined, the supposed dolomitic portion 
proves to be an intimate mixture of quartz and magnesite. 
