7 6 



University of California. 



[Vol. 2. 



which proved to be hypersthene diabase and epidiorite. These 

 lenses were believed to be portions of a dike intrusive in the serpen- 

 tine and broken up by a subsequent movement. F. L. Ransome* 

 has described the serpentine of Angel Island, and shown that it 

 originally consisted mostly of diallage. Inclusions occur here 

 also, but their nature and position are such that the conclusion was 

 reached that they could not be intrusions but fragments of an ad- 

 joining rock enveloped in the magma. 



Observation has shown it to be a fact that nearly all the numer- 

 ous bodies of serpentine have associated with them smaller masses 

 of feldspathic rock which vary in character from gabbro to diabase. 

 The relation of these feldspathic rocks to the peridotitic has been 

 very difficult to determine with certainty. This is due partly to 

 poor exposures, and parti/, perhaps chiefly, to the frequently dis- 

 turbed condition of the altered peridotites. Many of the largest 

 areas, namely, those at New Idria and Knoxville, have undergone 

 internal stress and shearing on an extensive scale, and as a result 

 have been reduced to shaly or even pulverent masses. Scattered 

 through these crushed areas are nodules of massive serpentine, and 

 lenses of a gabbroitic or diabasic character. These occur in a man- 

 ner similar to that described by Dr. Palache. The author f has 

 noticed and described the same condition of things existing on a 

 large scale near Knoxville, Lake County. Not only do there occur 

 here lenticular inclusions of what are without doubt foreign bodies 

 caught up in the magma, but also lenses of fine granular crystalline 

 rocks whose relations are puzzling. There are places, however, 

 where these lenses are clearly shown to be portions of disrupted 

 dikes, and it is probable that such is the character of the larger part 

 of similar occurrences. 



The dikes of diabase on the southern side of the Lion's Head 

 are very irregular, swelling out and then almost pinching. Should 

 movement take place along the sides of such a dike, it would be 

 broken up, and the fragments separated from each other would 

 present an appearance closely resembling foreign inclusions. Incip- 

 ient stages of this kind appear in the cliffs. In one case a compar- 



* Bull. Dept. Geol. Univ. Cal., Vol. I, p. 219. 



f Eleventh Report of the State Min. of Cal., pp. 69-71. 



