84 H. W. FAIRBANKS — GEOLOGY OF THE COAST RANGES. 



J. S. Newberry ^ says of the jasper about San Francisco : 



''Veins of white quartz, generally small, traverse it in every direction, and where 

 it is weathered it is often peculiarly cellular, ragged and rough. Where stratified 

 the laminae which it exhibits are twisted and contorted in all possible directions, 

 and, whatever is the history of the material of which it is composed, whether it is 

 thrown up from below or, as is more probable, it is a metamorphosed form of the 

 associated rocks, it is evident that it has been subject to a high degree of heat." 



Whitney t refers to the jaspers as silicified shales. 



They were first thoroughly studied by Dr Becker,^ who speaks of them 

 as " shales silicified to chert-like masses, of green, brown, red or black 

 colors, intersected by innumerable veins of silica." He says further : 



'' Under the microscope the most highly indurated specimens are found to con- 

 tain fossils." 



All observers seem to have noted the wavy, thin bedded structure and 

 the network of quartz veins. These characters are widespread, being ex- 

 hibited by the jasperoid rocks of the pre-Cretaceous series through their 

 whole extent in the Coast ranges. In the opinion of the writer, these 

 peculiar jaspers are confined to that series and form one of the means 

 by which it can be detected. The most striking outcrops with which 

 the writer is familiar occur in Red Rock canyon, eastern Santa Barbara 

 county, where an immense pinnacle of red jasper rises with precipitous 

 faces 200 to 300 feet. At nearly every locality where the pre-Cretaceous 

 series of rocks outcrops, from this point northward, the jasper is to be 

 seen. Red jasper of a similar character has been observed in Trinity 

 county and near the coast on the Oregon line. 



A number of slides were prepared from specimens collected from 

 different sections of the Coast ranges. A study of these showed the 

 existence of such a remarkable uniformity that one description will 

 answer for the essential features of them all. They consist of a minutely 

 granular aggregate of crystalline quartz, with varying proportions of 

 isotropic silica. The different colors are due to a varying amount of iron 

 oxide, the red varieties being so impregnated with it as to be almost 

 opaque. Minutely circular or elliptical areas, sometimes a millimeter in 

 diameter, but generally less, are scattered through the rock, sometimes 

 forming as much as a fifth of the total mass. By transmitted light these 

 spots are distinguished by being clearer than the rest of the rock, while 

 in polarized light they show a radial or granular aggregate of crystalline 

 quartz which in optical properties resembles chalcedony. In only one 

 slide w^as there noticed any traces of structure in these circular bodies. 



* Pacific Railroad Survey, vol. vi, p. 12. 



t Oeneral Geology of California, p. 66. 



J Geology of Quicksilver Deposits of the Pacific Slope, p. 106. 



