486 Tek WW, IC QURINIOIRe 
Professor Whitney, in the study of the Coast Ranges, came to 
the conclusion that the serpentine originated from the alteration 
of sediments. Dr. M. E. Wadsworth,* who studied the Whitney 
collection of rocks, however, subsequently described some of the 
serpentines and pyroxenites and peridotites from serpentine 
areas in California, as probably being igneous rocks. Professor 
Whitney, under whose supervision Dr. Wadsworth worked, does 
not appear to have objected to this. 
When Dr. Becker undertook the investigation of the geology 
of the quicksilver districts, the difficulty of accounting for the 
great change in chemical composition of any sediment to a rock 
with the composition of serpentine was very apparent. How- 
ever, he found evidence of such alteration in the sandstones of 
what is now known as the Franciscan or Golden Gate series. 
Some of these sandstones contain igneous material, derived 
undoubtedly from preéxisting igneous rocks or from volcanoes 
of the Golden Gate period, and some of this igneous material 
undoubtedly has formed some serpentine. Indeed, needles of 
serpentinoid material were noted eating their way into grains of 
quartz, and such evidence led Dr. Becker to conclude that con- 
siderable masses of serpentine were thus formed. He suggested 
that sufficient magnesia for such a metasomatic change might be 
derived from the micas of the granites which underlie the Coast 
Ranges. Dr. Becker? later (1893), however, regarded some of 
the serpentine masses described in the quicksilver monograph as 
being altered peridotites. 
In my field work at Mt. Diablo I came to the conclusion that 
the serpentine there is of igneous origin, as I found traces of 
the original pyroxene and olivine of the peridotite from which 
the serpentine was derived at several points. Dr. Charles 
Palache, in his bulletin on the rocks of the Potrero, San Fran- 
cisco, likewise concluded that the Potrero serpentine is of igneous 
origin, and Dr. Ransome treated the serpentine of Angel Island 
*Lithological Studies. Memoirs Mus. Comp. Zodl., Vol. XI, It IE, Os W2O, 132, 
142 and 158. (See also general discussion of the origin of peridotite, pp. 189-192.) 
? Mineral Resources of the U.S. for 1892, Day, p. 144. 
