298 The American Geologist. May, 1894 
this older folded series. .They are also usually unaltered, and 
almost never contain metalliferous deposits. 
The igneous rocks may be classified as intrusive and effusive. 
but some of the fragmented diabases and porphyrites that are 
included under intrusives were undoubtedly surface rocks. 
Intrusive. 
Amphibolite. 1 
Diabase and porphyrite. 
Homblende-uorphyritfi.* i> • 
, , , , , l ' ■ Basic series. 
( rabbro and nonte. 
Peridotite and pyroxenite. 
Diorite. 
Granodiorite. ) 
( Sranite-porphyry. 
Biotite-hornblende-granite. Acid series. 
Quartz-porphyrite. 
Quartz-porphyry. 
Effusive. 
Rhyolite. 1 
Hornblende-mica-andesite. 
Hornblende-pyroxene-andesite 
Pyroxene-andesite. 
Acid series. 
older basalt. 
I )olerite. Basic scries. 
Other late basalts. I 
INTRUSIVE IGNEOUS ROCKS. 
Amphibolite. 
The rocks here designated as amphibolite appear all of 
them to have been derived by metamorphism from igneous 
rocks. The amply bolites may be classified under three head- 
ings : massive amphibolite, amphibolite-schist and amphibole- 
talc rocks. 
Massive amphibolites. Under this head are placed certain 
granular amphibolites which are known in certain cases to 
have resulted from the alteration of pyroxenites. No. 240 
Amador county and No. 76 Calaveras county are examples. 
Amphibolite-schist. The majority of the green schists so 
abundant in the gold belt are amphibolites, derived as lias 
been shown by the microscope and by field observations, very 
largely from rocks of the diabase series by dynamometamor- 
phism. The augite of the original diabase may frequently be 
-ecu altering into fibrous green hornblende. There is usually 
in these schists secondary feldspar and quartz, with a good 
*Some of the porphyrites contain over 60# of silica and therefore be- 
long to the acid series. 
