346 University of California Publications in Geology [Vol. 11 



merits of the rock, so as to isolate them from the adjoining portions. The flat 

 surface of one of the specimens, when viewed at a short distance, appears as if 

 covered by a tangled mass of white cord. 107 It is probable that these flinty 

 strata are similar to those seen by Professor Dana, and described in his report as 

 prasoid rocks. 



Although the direct transition from the unaltered sandstone and shale to these 

 metamorphic strata has not been observed, there is little doubt that they are of 

 the same formation, and that the jaspery condition is due to igneous agencies. 

 The chemical composition of the sandstone and the shales is favorable to such a 

 result. It is regretted that analyses of each, and of the metamorphosed portions 

 cannot be presented. 



In another place Blake 108 writes as follows : 



At several places on the peninsula of San Francisco a peculiar, hard and 

 flinty rock appears at the surface, and exhibits distinct stratification. It has a 

 variety of colors, but a dark reddish brown is the most common. It is much 

 traversed by irregular veins or seams of quartz, and has a banded or belted 

 structure, so that it resembles varieties of jasper ... all the characters of this 

 rock, and its positions, indicate that it is an altered portion of the San Francisco 

 sandstone formation. 



J. S. Newberry 109 described the occurrence of jasper at a number 

 of localities around the Bay of San Francisco, and suggested two pos- 

 sibilities in explanation of their origin : 



... It frequently occurs in ridges, having the appearance of an erupted rock, 

 protruded along lines of upheaval. It is red, yellow, or green in color, but often- 

 est blood-red, or some intermediated shade between that and pink, being usually 

 somewhat mottled, clouded, or striped. 



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 subjected to a high 

 degree of heat. These jaspery rocks are, equally with the serpentines, a marked 

 feature of the geology of the Coast Ranges, from the Gulf of California to the 

 Columbia. 



In 1865, Whitney published descriptions of the Coast Range 

 formations in The Geology of California. In describing the radio- 

 lariart cherts of Mount Diablo, he says : 



On the outside of this great central metamorphic mass, both on the north and 

 south, but not entirely surrounding it, are heavy accumulations of jaspery rock, 



107 See plate 31c. 



ids Observations on Physical Geography and Geology of the Coast of Cali- 

 fornia from Bodega Bay to San Diego, U. S. Coast and Geod. Surv. Bep. 1855, 

 App. no. 65, 1856. 



loo Pacific Bailroad Bep. V, Geological Beport, p. 12, 1856. 



