KhOGKS OF THE COAST: RANGES OF CALIFORNIA 401 
appears to me, in view of the foregoing facts, that it is yet to 
be demonstrated that these schists are the result of contact 
metamorphism of the peridotite intrusions. In any (casey) at 
seems clear that the glaucophane-schists and the green amphi- 
bole, garnet, and micaceous schists associated with them, are all 
caused by the same kind of metamorphism. 
An investigation of the geology of the Bidwell Bar quad- 
rangle, in the northern Sierra Nevada, has brought to light the 
existence of large areas of magnesian schists, associated with 
serpentine. These magnesian schists are composed of talc, 
chlorite, and various amphiboles, among which are prominent 
certain colorless amphiboles approximating to edenite and ged- 
rite in composition. The microscopic investigation of these 
rocks clearly shows that these magnesian schists are alteration 
products of rocks of the same general nature as those which 
form the serpentine; that is to say, of rocks of the pyroxenite- 
peridotite family. The serpentine itself, no doubt, was largely 
formed from those masses rich in olive or rhombic pyroxene, 
and the various schists from aluminous pyroxenic facies of the 
magma. Many of these masses form croppings in and along 
serpentine masses, but they also form isolated areas of consider- 
able extent. To conclude that any of these schists were formed 
by contact metamorphism would certainly in this case be errone- 
ous, for not only can their composition be accounted for by sup- 
posing them to be alteration products of various pyroxenes, but 
their formation from these pyroxenes can in many cases be seen 
in the thin sections of the rocks. 
If, as thought by Fairbanks, the Franciscan or Golden Gate 
series is older than the Knoxville, its generally hardened and 
altered character may have been the result of a pre-Knoxville 
metamorphism; for the beds, which have been deteimined as 
Knoxville, are nowhere much altered. It may then be advanced 
as a working hypothesis that the entire schist series of the 
Golden Gate formation was formed before the deposition of the 
Knoxville, and before the intrusion of at least some of the ser- 
pentine. If this be true, pebbles of some of these schists should 
