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University of California. 



[Vol. 2. 



which the various rock masses bear to each other. At the sugges- 

 tion of Professor Lavvson, to whom I would also acknowledge 

 many obligations for assistance, the work which is here outlined 

 was undertaken, its specific object being to determine more defi- 

 nitely the important physical and chemical properties of some of 

 the most striking species of local occurrence. The specimens 

 used in the investigation were all obtained from either one of two 

 localities in the Berkeley Hills immediately east of the Bay of 

 San Francisco, one (designated as locality A) near the northern 

 limits of the town of Berkeley and the other (designated as 

 locality B) not far from, and to the south of, the village of San 

 Pablo. 



A GREEN HORNBLENDE. 



Occurrence. — This mineral is found in both the localities cited. 

 At the former station it occurs in the form of loose boulders, 

 within an area of schists and serpentine. These boulders are from 

 ten to thirty centimeters in diameter, and consist of coarsely 

 crystalline, compact masses of the green mineral, the interstices 

 between the crystals being filled with either talc or chlorite, only 

 one of the associated minerals being present in the same boulder. 

 In some instances the boulders are composed of pure hornblende, 

 and in no instance do the associated mineral form any considerable 

 percentage of the entire mass. The second occurrence of the min- 

 eral presents essentially the same features. The boulders are here 

 distributed over a considerable area characterized by the presence 

 of crystalline schists, of serpentine, and of various alteration 

 products of the latter. Though the majority of the boulders are 

 small and present only rounded and polished surfaces, masses of 

 angular form whose longest dimension exceeds 75 centimeters 

 were several times observed. As in the former locality, they were 

 in all cases coarsely crystalline, the individuals often attaining ten 

 centimeters in length and several millimeters in their longer diameter; 

 chlorite was here the more common associate. Frequently indica- 

 tions of a schistose structure were shown by the manner in 

 which the boulders cleave on breaking; in other instances definite 

 crystal centers could be recognized, but in many cases no especial 

 orientation of the constituent crystals was to be observed. 



