1904.] HAEHL AND ARNOLD — THE MIOCENE DIABASE. 39 



Fig. 19. Spheroidal weathering of the diabase exposed beside the Page Mill 

 road, one-half mile east of the summit, x jq. Photo, by R. Arnold. 



ing the white feldspars but indistinctly, the predominating crys- 

 tals being augites and olivines. The finer grained varieties make 

 up the larger masses, such as the tuffs and some of the dikes of the 

 Langley Hill-Mindego Hill igneous area, and are often amygda- 

 loidal, weathering into a compact adobe soil. Amygdaloidal cav- 

 ities of great size are frequently encountered. One cavity filled 

 with quartz measured four inches along its greatest diameter. Cal- 

 cite, chalcedony and serpentine fill the cavities in many in- 

 stances, and on Bogess and Harrington Creeks diabase in place was 

 found with its vesicles filled with petroleum. Perhaps the most 

 interesting occurrence is the presence in many places of nests 

 of glassy analcite crystals, filling the amygdaloidal cavities and 

 joints and seams in the rock. Almost perfect icositetrahedrols 

 were obtained. Qualitative tests showed the presence of Al, Naand 

 SiOj. The mineral is fusible before the blowpipe and soluble in 

 hydrochloric acid, yielding no jelly, however; in this particular 

 agreeing with the observation made by Lawson and Palache^ on 



i"The Berkeley Hills," Bull. Dept. Geol. Univ. Cul., Vol. II, p. 418. 

 Berkeley, 1902. 



