SLOIDILES ION JIE, IMIR OCIIINIS, QUE CAULIUTONIMICA. 437 
younger than the limestone and the other metamorphics. The 
cherts have been described by Mr. Becker under the name of 
phthanites,* and more recently by Mr. F. Leslie Ransome as 
radiolarian cherts.*. They are usually dark brown, thin bedded, 
much contorted siliceous rocks, very characteristic wherever 
found in the Coast Ranges. The only fossils thus far found in 
them are Radiolaria, and these have led to the belief that the 
rocks are of Jurassic or Cretaceous age. In connection with the 
radiolarian chert there frequently occurs a metamorphic sand- 
stone, ranging in color from light yellow to dark brown. It 
usually shows evidence of having been subjected to agencies 
which have obliterated nearly all bedding planes, produced sec- 
ondary silicification, and frequently reduced the whole to a struc- 
tureless mass. 
In various parts of the range are considerable areas of ser- 
pentine and kindred rocks. The origin of this serpentine has been 
the subject of much discussion. There can now be no doubt 
but that it is a decomposition product of peridotes and other 
igneous rocks with which it is associated. 
The relation of the metamorphic rocks to each other and to 
the younger rocks is very obscure, and the subject will not be 
taken up here. 
THE PESCADERO SERIES. 
The San Francisco sandstone was one of the earliest forma- 
tions recognized and described in California. By Professor 
Blake it was assigned to the Tertiary.3 It was later found that 
the fossils upon which his conclusions were principally based 
came from the Pliocene of the Merced series. Professor Whitney 
called the formation Cretaceous, classing the metamorphic rocks 
with it. Recent writers have thought the metamorphics and 
San Francisco sandstone pre-Cretaceous.5 The writer has been 
able to verify Professor Blake’s first conclusion. The sandstone 
tMonograph XIII., U. S. Geol. Sur., 1888. 
2 Univ. of Cal., Bull. Dept. Geol., I., T99-200. 
3 Rep. Geol. Recon. of Cal., 1858, p. 153. 
4Geol. Surv. of Cal., Geology, I., 77, 24, etc. 
5 American Geologist, IV., March, 1892, 133. 
