6 B. Silliman on the Deep Placers of 
sizé, undergo a similar slacking by atmospheric action, even in 
a very brief period of time, rendering it almost impossible to 
preserve specimens of the gravelly concrete unless they are pro- 
tected by varnish. The most unyielding of the ‘cement’ masses 
are sometimes left over one season by the miners, exposed to the 
air and frost, to secure the benefits of this disintegration, without 
which but little of the contained gold can be obtained. 
The gold is disseminated throughout the entire mass of this 
t gravel deposit, not uniformly in value, but always in 
greater quantity near its base or on the bed rock. The upper 
half of the deposit is found to be always less in value than the 
lower part, sometimes so poor that it would be unprofitable 
working by itself, but inasmuch as there is no practicable mode 
of working the under stratum without first moving the upper 
portion, in practice the whole is worked. 
The gold rarely occurs in large masses in this ancient gravel. 
Often on the polished and very smooth surfaces of the ‘bed 
rock’ and of the superincumbent masses of gravel when freshly 
raised from their long resting place, the scales of brilliant 
yellow metal are beautifully conspicuous. These are frequently 
idea of the remarkable features of this ancient floor, moulded 
and rounded by water or ice, as a series of good stereoscopic 
the kind assistance of Mr. C. F. Watkins, of San Francisco, so 
well known for his admirable California views. The “bed rock” 
varies of course in different portions of the area now under con- 
sideration, being either granite, gneiss, greenstone or shale. In 
the granite are observed numerous minute quartz veins pursuing 
a course parallel to each other often for hundreds of feet without 
interruption. 
In the ‘American Claim,’ at San Juan, the granite is suc- 
ceeded on the west by a large jointed blue siliceous shale, of the 
same strike with the main joints of the granite. This latter 
‘ock 1s covered by numerous very boulders of meta- 
morphic conglomerate, of which no traces are seen in place. 
* 
bea 
Sar 
ee fA Sone ee ich 
