Anderson.] 



Point Reyes Peninsula. 



of this pre-granitic crust. At least two members of this ancient 

 series have probably been recognized in this field. 



Marble. — Immediately west of Point Reyes Station, upon the 

 crest of the ridge, is a body of white, crystalline limestone which 

 has at some time been used to a limited extent for making lime. 

 It is almost pure white and highly crystalline. It contains 

 numerous scales of graphite disseminated through it in clusters 

 and patches. The best exposure of it is on the "old road" which 

 crosses the summit from the .head of Tomales Bay. The area 

 is of limited extent and forms an irregular S-shaped body whose 

 longer axis is not greater than one mile and whose width is per- 

 haps one-fourth of a mile. It is the body of marble that was first 

 described by Whitney as a feature of the peninsula. 



The following is a rough analysis of a sample of the purer 

 quality of it: — 



CaC0 3 97-50% 



MgC0 3 1.60" 



Fe 2 3 35" 



Insoluble residue 1.10" 



100.55% 



This rock is similar to the white crystalline limestone of Montara 

 Mountain mentioned by Professor Lawson. 1 It occurs also at 

 Santa Cruz, and still more abundantly in the Santa Lucia Moun- 

 tains, extending along the coast south of the Bay of Monterey. 



Qnartzite. — At the summit of one of the northern spurs 

 of Vision Hill south of Inverness, there is an exposure of a very 

 hard, dark gray, vitreous rock that under the microscope proved 

 to be a fine-grained quartzite. The grains are small and rounded 

 and closely crowded upon one another. They are quite clear, 

 except that they contain a great many inclusions of iron oxide and 

 other crystalline particles. Small fragments of both biotite and 

 hornblende occur among the grains of quartz. No limestone 

 or calcite was noticed in any connection with this rock, and 

 no evidence of stratification was observed, though both of these 

 might have been found, with sufficient searching. 



l i5th An. Rept. U. S. Geol. Sur. 1895, p. 414, etc. 



