328 University of California Publications. [Geology 



of the pits and chambers which characterize the weathered ex- 

 posures of this phase of the blout quartz, remnants of limestone 

 may be occasionally detected. In one case a mass of limestone 

 about 8 inches in diameter showing abundant traces of fossils 

 was found imbedded in the quartz at the bottom of a depression. 

 In other cases the presence of the carbonate in such situations 

 was proved by effervescence on the application of dilute acid. 



The third general variety of blout quartz shows a pronounced 

 breceiated structure, the whole being made up of sharply angular 

 fragments, mostly less than an inch in diameter but often as 

 much as three or four inches. The breccia is generally well 

 cemented, and firmly bound together. The cementing material 

 in most cases observed is quartz, but in some cases where the 

 breccia has been exposed to the weather, the cement is etched, 

 leaving the angular fragments in sharp relief. In these cases 

 the cement proved to be, in part at least, carbonate of lime by 

 testing with dilute acid. In the breccia with siliceous matrix 

 the angular fragments are often free of color while the matrix 

 is strongly colored by iron oxide and appears as a compact red 

 or yellow jasper. All three of these varieties of blout quartz may 

 occur together in the same mass. 



The stratiform facies of the solid compact variety of the 

 quartz has been alluded to. But the cavernous and breceiated 

 varieties are often also stratiform. In this case the stratification 

 is so similar to the stratification of the neighboring limestones, 

 that no one in the field could have any doubt but that the quartz 

 is the result of the silicification of that formation. Not only is 

 the quartz stratiform, but the individual beds are quite distinct 

 from one another and separate under the weather along the 

 original bedding planes. "When in such stratiform quartz, re- 

 sembling an outcrop of limestone, one finds residual masses of 

 fossiliferous limestone imbedded in it, in the bottom of depres- 

 sions due to weathering, the evidence amounts to a demonstra- 

 tion that some of the blout quartz at least is the product of the 

 silicification of the limestone adjacent to the intrusive porphyry. 



This conclusion cannot, however, be extended with certainty 

 to the solid, compact varieties of the blout quartz, which make 

 up the greater part of the occurrence, and the stratiform appear- 



