3904.] 



HAEHL AND ARNOLD — THE MIOCENE DIABASE. 



37 



tinguishable. One, augite, is present in dark patches intruded by 

 the others, and showing distinct glistening cleavages. Magnetite 

 can be detected in large flat plates and smaller grains, dark and 

 lustrous. Separated with a knife-blade, small portions can be picked 

 up readily with a magnet. The most evident component is the 

 feldspar. It occurs in long white rod-like crystals sometimes as 

 iiiuch as two inches in length, giving a reticulated appearance to 

 the mass; it is banded and contains inclusions of magnetite and 

 augite. Fig. i8^ is a photograph of the typical diabasic facies, 

 being specimen No. 24, the analysis of which is given as I in a 

 following paragraph. 



Fresh specimens showing but slight kaolinization are readily ob- 

 tained. Occasionally a crystal is seen to contain a few clear, glassy 

 spots quite easily distinguishable with a hand lens. They are prob- 

 ably analcite. 



Fig. 18. (a) Showing the basaltic (specimen 38) and {/>) true diabasic (speci- 

 men 24) facies of the diabase. Reduced one-half. Photograph by Ralph 

 Arnold. 



On the stage road from Redwood City to La Honda, at a point on 

 the west side of the summit, about one-half mile from the Summit 



