Vol. 5] 



Louderback. — Bcnitoite. 



337 



The outcrop occurs on a hill which, as shown in plate 28, is 

 separated from the neighboring ridge by erosional depressions 

 on all sides. Practically all of the country in view in this photo- 

 graph, which was taken looking a little east of north, is serpen- 

 tine, including the basal portion of the mine hill. The rock 

 mass directly associated with the veins lies along the top of 

 the hill from a point directly below A to one directly below B, 

 and is about 520 feet long, and perhaps 400 feet in its widest 

 part. 



The outcrop of the mineralized belt lies entirely on the side 

 of the summit visible in the photograph and extends along a 

 line determined in the photograph by the right end of the cut 

 and top of the dump. It is a zone of veination which consists 

 of a large number of irregular stringer-veins running along- 

 together in the general direction of elongation of the zone, and 

 connected by many branches and anastomosing laterals. The 

 rock in the vicinity of the veins is altered by recrystallization, 

 metasomatosis, and impregnation, in some places porous from 

 solution of certain constituents, in others tough and cemented 

 by natrolite impregnation. 



EFFECTS OF EARTH MOVEMENT AND PEESSUEE. 



Considerable movement has taken place both before and since 

 the mineral deposition, and it is distinctly concentrated along 

 the mineralized zone. The great majority of the planes of move- 

 ment and crushing lie in or near the plane of strike of the zone 

 of mineralization, but a few are transverse. 



The effects of pressure may be tabulated : 



!1. Local schistosity. 

 2. Cra-cks and spaces giving loci of veins 

 and druses. 



( 3. Sheeting, crushing, and breeciation. 

 Subsequent to deposit. < . -m , -.. , , - 



M 1 I 4. Faulting and displacement or veins. 



In the first three of these groups the planes lie approximately 

 in the zone of mineralization. A few of the later fault-planes 

 are transverse and have displaced the veins and rendered the 

 deposits more or less discontinuous. 



The appearance of schistosity in the massive rocks seems 

 to be limited to the immediate vicinity of the zone of veination 



