320 The American Geologist. May, 1893 
strata and the metamorphics of mount Diablo mentioned by Mr. 
Becker as a proof of the unity of the two formations. " 
Mr. Faii'banks' description of his "best contact" in the above 
paragraph seems certainly to appl}' not to an unconformity, but 
to a fault which perhaps might as readily occur between 
metamorphosed and non- metamorphosed beds of the same age as 
of different ages. 
On page 164, the serpentine of the Coast ranges is referred to 
and all considered as resulting from the alteration of basic 
igneous rocks. This was shown to be true b}' the writer of the 
serpentine of mount Diablo and from specimens in the National 
Museum it appears to be likewise true of the serpentine of the 
San Francisco peninsula and of New Almaden. It has been like- 
wise clearly shown to be true of the serpentine of the Sierra 
Nevada by Mr. Diller, Mr. Fairbanks, and the members of the 
California Division of the United States Geological Survey. 
However, it has been proved by micro-chemical and micro- 
optical tests b}^ Messrs. Becker and Lindgren* that various 
minerals in the Coast range sandstones are altering to serpentine 
and it is the opinion of Dr. Becker that this metamorphism has 
resulted in forming considerable bodies of serpentine. 
Mr. Fairbanks concludes his paper with the following, pp. 165 
and 166: "From the foregoing illustrations coupled with my own 
observations I think we can safel}' say that no important non- 
conformity exists in the Cretaceous and that it is utterly impos- 
sible that the great upheaval of the Coast ranges could have 
taken place at the close of the Gault or Shasta period, as Dr. 
Becker has lately affirmed. A small unconformity undoubtedly 
exists due in part to the eruption of the serpentine and in part 
to an uplift accompanying it. The extrusion of such an immense 
body of igneous rock as that near Knoxville, ranging from three 
to five miles in width and twenty miles long, must have pushed 
back and tilted the Knoxville shales to a considerable extent." 
While there is thus evidence that the main metamorphism of 
the Coast range rocks occurred before the deposition of the Knox- 
ville beds there is here granted by the author a post-Knoxville 
disturbance accompanied by the extrusion of serpentine. Now 
serpentine is a very abundant rock in the Coast ranges. It occurs 
almost everywhere associated with the phthanites, hardened 
^Monograph on the Quicksilver Deposits, pp. 122-126. 
