Gold-Beariug Lodes in California. — Hcrsliey. 85 
found both in the schist series and the serpentine, and are not 
always parallel to the strike of the strata. Their identification 
as intrnsives is further strengthened by their variation from an 
apparent homogenous, fine-grained white quartzyte, to a true 
porphyritic character by the appearance of crystals of feldspar 
or of hornblende, or more often by the separation of some of 
the free quartz into distinct crystalline individuals. As several 
of these quartzyte-like dikes carry gold in certain mines, they 
are of considerable importance to the student of mining geol- 
ogy- 
Dioryte. — Under this heading I include a rather coarse- 
grained aggregate of distinct crystals of dark green and black 
hornblende and plagioclase, constituting a crystalline of gray 
and greenish gray color which occurs in large masses of ir- 
regular shape along a belt following ihe southeastern slope of 
the Sierra Costa mountains eastward from the main Trinity 
river, being apparently intruded into the serpentine near its 
junction with the so-called "picrolyte." Cy the addition of 
free quartz and the replacement of the plagioclase by ortho- 
clase, it becomes a typical syenyte which appears as dikes in 
the serpentine and, I think, in the "picrolyte." I am inclined to 
consider this dioritic and syenitic series of intrnsives as the 
deep-cooling portion of the great diabase and porphyryte for- 
mation of the Jurassic area nearby, but cannot as yet prove 
this connection. However, it is nearly certain that they be- 
long to a much earlier period of volcanic activity than that of 
early Cretaceous age to which the granites are referable- 
Dioryte-porphyryte. — Two distinct systems of intrnsives 
come under this heading. One is characterized by needle- 
shaped crystals of dark green and black hornblende embedded 
in a fine-grained aggregate of hornblende and |)lagioclase in- 
dividuals. The general color of the rock is dark greenish 
gray to black. It constitutes a series of dikes which have a 
prevailing east-west course in sharp contrast to the prevailing 
north-south course of nearly all the other trappean systems of 
the region. It is younger than the granitic series; it cuts the 
granite-porphyry and the pegmatyte dikes of the Upper Coffee 
creek region, but its relation to other systems is not yet clearly 
worked out. 
There is another anel apparcntl\' later system of dikes of 
