I9I0-] COAST RANGES OF CALIFORNIA. 321 



still recognizable, bastite being the most resistant. The silicious 

 substance assumes a red or yellow color upon weathering, due to the 

 oxidation of iron compounds, and finally crumbles away. This 

 feature of the rock is fully described by A. Knopf.^ 



The serpentine is associated with a coarse-grained somewhat 

 metamorphosed sandstone, in which biotite is prominent and which 

 in places assumes the character of a fine-grained conglomerate. To 

 the south of the first belt where the Manzanita Mine is located shales 

 are found. The sandstone, according to G. F. Becker, is of Knox- 

 ville age.^° This he substantiates by the finding of impressions of 

 AitccUa Piochii in the metamorphosed rock close to the ]\Ianzanita 

 ]\Iine on Sulphur Creek. Although no direct contact was observed 

 by the author, it being covered by soil and brush, the approximate 

 contact is marked by a more intense degree of metamorphism of 

 the sandstone. It is here exceedingly hard and responds to the 

 blow of the hammer with a metallic ring. In the bed of Sulphur 

 Creek was also seen serpentine which carried angular fragments 

 of the sandstone. 



The contact metamorphism is not accompanied by crystalline 

 schists, but is such as would be caused by a strong thermal action. 



II. The Knoxville and Clear Lake District Serpentines. 



The Knoxville Serpentine. 



The district as has been defined is the strip of country bounded 

 in the north by Cache Creek and in the south by Putah Creek. Its 

 principal body of serpentine which covers an area of approximately 

 forty square miles is perhaps the largest found in the cntral coast 

 ranges. A narrow strip a few hundred feet wide runs parallel to 

 Perkins Creek, two miles south of it. Crossing Cache Creek it 

 broadens out, capping the ridge that has its highest point a mile 

 southwest of the Shamrock ]\Iine. At this point the serpentine has 

 a width of about one mile. ^Maintaining this width, it follows 



'A. Knopf, "An Alteration of Coast Range Serpentine," Bull. Dcpt. 

 Geol. Univ. Cal, IV., 425, 1906. 



" G. F. Becker, " Quicksilver Deposits of the Pacific Coast," ]\Ionograph 

 XIII., U. S. G. S., 183, Washington, 1888. 



