Gold "Pockef Deposits in Northern California. — Hershcy. 39 
row river valleys whose floors have an average altitude be- 
tween 2,000 and 2,500 feet. On the eastern side is the main 
Trinity range, forming the watershed between the Klamath 
and Sacramento river systems, and reaching altitudes of 4,000 
and 5,000 feet. It is this regio'n of lower mountains, crooked 
river valleys and deep gulches, lying east of the White Granite 
peaks, that is preeminently the "pocket" country of Trinity 
county. 
The geologic structure of these mountains is remarkably 
simple. There is a basement rock series of igneous or ancient 
cjuasi-volcanic material. Its prevailing characters on outcrop 
in the area under discussion are those of a compact, fine-grain» 
ed, dull green massive rock closely resembling certain varieties 
of diabase. When exposed it has a ragged appearance because 
of extensive jointing, but it lacks the stratification lines of slate. 
Near the surface it is very frequently amygdaloidal, the orig- 
inal rounded cavities being now filled with white cjuartz. Sev- 
eral hundred feet below the top of the formation it becomes 
coarser grained, and finally passes into a coarsely crystalline 
rock of gray color, and an appearance like dioryte. The thick- 
ness is unkno\\'n but is at least 1,000 feet as that amount is ex- 
posed without any otlier appearing under it. In age it is prob- 
ably Jurassic. 
Resting upon the igneous formation is a series of alter- 
nating thin-bedded black slates and thick-bedded blue quartz- 
yte, which collectively constitute the Black Slate formation, 
also of probable Jurassic age. In general, the slate formation 
remains practically in its original horizontal position except 
that it is gently arched with an axis along the summit of the 
Trinity range; but, considered in detail, it is much disturbed by 
faults and irregular folds of small dimensions so that locally it 
presents dips of high degree, in not a few cases vertical and 
even overturned. The igneous formation has participated in 
these disturbances to a certain extent so that the contact be- 
tween the two varies as much as 600 or 1,000 feet in altitude 
between the two sides of a narrow ridge. In the valley of the 
Trinity river, the contact line averages several hundred feet 
above the stream level between Trinity Centre and Eastman 
gulch, but in places rises to 700 or 1,000 feet and in others the 
black slates come down to the river level. But. disregarding 
