W. Lindgren — Gold Deposit at Pine Hill, Gal. 93 



The deposit to be described here differs strangely from the 

 common type. Pine Hill is situated about eleven miles south- 

 southwest of Grass Valley, in Nevada County, and a few 

 miles north of Bear Kiver ; it is in the lower rolling foothills 

 of the Sierra, and the summit of the little knoll bearing the 

 above name rises to eighteen hundred feet above the level of 

 the sea ; from the top an extensive and beautiful view is ob- 

 tained westward over the Sacramento valley, and eastward 

 toward the crest of the snowy range. 



m 



s 



A B CD 



Sketch of Pine Hill and vicinity, Nevada Co., Cal. 



Scale 2 inches = 1 mile. Contour Interval 100 feet. 



A. Diabase or Porphyrite. B. Decomposed Zone. 



C. Serpentine. D. Quartzite and Slate. 



Toward the south and west a large area extends occupied 

 by massive diabases and diabase porphyrites in which aurifer- 

 ous veins are but seldom met with ; to the east of Pine Hill 

 there is a somewhat complicated area of quartzites and clay 

 slates, serpentines and gabbros sometimes dynamically metamor- 

 phosed and containing a few veins of gold quartz, usually very 

 capricious as to the distribution of the metal. A part of this 

 area is shown on the sketch. To the northwest, beyond the 

 limits of the map, there is a large and massive area of granite, 

 diorite and gabbro with very few auriferous deposits. 



The diabase and diabase porphyrite which form the prevail- 

 ing rock of the vicinity, are massive, fine grained and not a 

 little affected by secondary processes giving rise to uralite, 

 chlorite, secondary quartz, etc. The diabase porphyrites 

 appear to prevail along the crest of the ridge, of which Pine 



