488 EL, WE DOTNET 
as a metamorphosed igneous rock. The Angel Island rock was, 
however, considered as possibly being derived chiefly from dial- 
lage, but the analysis given shows clearly that no such deriva- 
tion is possible. The table of analyses given below indicates 
how uniform in chemical composition the serpentines of the Coast 
Ranges are, and also that olivine or rhombic pyroxine must have 
been a prominent constituent of all of the original rocks from 
which the serpentines analyzed were derived. 
The Franciscan or Golden Gate formation.—The metamorphic 
rocks of the Coast Ranges, and the associated cherts, sandstones, 
and shales, were formerly considered as of the age of the Knox- 
ville beds; that is, lower Cretaceous. The more highly metamor- 
phosed of these rocks are green amphibolite-schists, blue amphib- 
olite-schists (glaucophane-schists), mica-schists, chlorite-schists, 
and various other schistose rocks. In my bulletin on Mt. Diablo, 
it was assumed that the red cherts or jaspers were silicified 
shales, and that these jaspers, together with the sandstones and 
schists associated with them, were the result of regional meta- 
morphism of the Knoxville formation. Since that time it has 
apparently been shown, chiefly by Dr. H. W. Fairbanks, that 
these jaspers, associated sandstones, and schists are older than 
the Knoxville beds, and probably of Jurassic age. The best 
description of this series of rocks is that by Professor A. C. 
Lawson in his “Sketch of the Geology of the San Francisco 
Peninsula.’’? . 
One of the most interesting rocks of the series is the blue 
amphibole-schist, which is often found in croppings in or near 
serpentine masses. The blue amphibole is perhaps in part glau- 
cophane, and these rocks have, therefore, generally been called 
glaucophane-schists. Dr. Ransome, in his study of the geology 
of Angel Island, found these schists at so many points on the 
border of serpentine masses that he concluded that they were 
contact metamorphic rocks. Professor Lawson, in the paper 
above referred to, considered the schists rich in amphibole to be 
metamorphosed volcanic material, but ascribed their origin, in 
t Fifteenth Ann. Rept. U.S. Geol. Surv. 
