426 



University of California Publications. [Geology 



properties, together with a fibrous habit, unquestionably identify 

 the mineral as bastite. The presence of chrome micas was sus- 

 pected, but could not be verified. 



The rocks under discussion have an extensive distribution in 

 the hills north of Berkeley, occurring as lenticular masses in the 

 Franciscan sandstone. The invariable presence of glaucophane 

 schists is suggestive. They occur at numerous other points 

 throughout the Coast Ranges, and are locally known as "the 

 quicksilver rock," on account of their frequent association with 

 cinnabar deposits. They were described as forming a subordi- 

 nate member of the Franciscan series (lowermost Cretaceous?), 

 and were provisionally designated as a silica-carbonate sinter.* 

 This was attacked by Fairbanks, t and in particular the sugges- 

 tion that the formation might be used in correlating isolated 

 portions of the Franciscan. His contention was based on the fact 

 that the rock occurs as the gangue of the quicksilver ores which 

 are k~\own to be of post-Miocene age, and that the silica-carbonate 

 sinter may, therefore, occur at any stratigraphic horizon. 



Becker,^ however, seems in part to have recognized the deriva- 

 tive origin of the rock under consideration, but his views are 

 largely obscured by his conceptions of the metamorphic char- 

 acter of the Coast Range serpentines. Von Groddeck,|| in a 

 remarkable paper on the Quicksilver Deposits at Avala, Servia, 

 was the first to draw attention to the pseudomorphic character 

 of the ore rock at New Almaden. 



His conclusions, both as to the Servian and California occur- 

 rences, were vigorously denied by Becker. 



The recent finding near North Berkeley of some exceptional 

 material allows the origin of the carbonate rock to be fixed 

 beyond question. 



Under the microscope a thin section of typical carbonate rock 

 is seen to consist of an intimate mixture of lime-magnesia carbon- 

 ates and chalcedony. The carbonates are without crystalline 

 boundaries and are frequently stained with yellow iron oxides. 

 The unusually strong differences of relief for and E indicate 



* A. C. Lawson, 15th Ann. Kept. U.S.G.S., pp. 435. 

 t H. W. Fairbanks, Jour. Geol. V. 63-67, 1897. 

 X Monograph XIII. U.S.G.S. 

 II Zeit. for Berg, Hutten-u-Salinenwesen, vol. 33. 



