338 



University of California Publications. 



[Geology 



and the planes of schistosity lie roughly parallel to the outcrop. 

 This is especially noticeable at the east end of the zone where 

 the rock is a fine-grained greenstone, and along the line of the 

 zone shows incipient schistosity and is traversed by narrow veins 

 of natrolite lying chiefly in the planes of foliation. 



The cracks and spaces in which the veins have been deposited 

 are not always completely filled, and drusy cracks and geodal 

 cavities are quite common. As might be expected, many of the 

 best crystals, and almost all of the better specimens, are ob- 

 tained from such drusy spaces. Often the filling has proceeded 

 so far that while a number of the crystals from opposite walls 

 have united, the majority are still free. These may be split 

 open. Plate 29 shows a slab three feet long and eighteen inches 

 maximum width which has been so opened, exhibiting the cor- 

 responding drusy surfaces. Plate 30 and plate 33 show smaller 

 surfaces more in detail. 



Sheeting is very marked in the face of the open cut, as can 

 be distinctly seen in plate 31. To the right of the rope it is 

 very well developed with vertical planes. It occurs in other 

 parts of the mine also. Crushing is evident here and in other 

 places where sheeting is not developed. 



It is interesting in this connection to note that eastward 

 beyond the limits of the vein-bearing rock-lens, and in continu- 

 ation of the direction of the zone of mineralization, the serpen- 

 tine is badly brecciated. 



Evidences of movement are very plentiful — both fault-planes 

 and displacements. In the face of the open cut (plate 31) the 

 rope lies on a very distinct plane of movement. To its right 

 is crushed, sheeted, and altered greenstone ; to the left the vein- 

 stone and tough impregnated wall-rock is seen broken into sep- 

 arate blocks. 



This crushing and faulting of the mineralized zones allows 

 the ready seepage of water, and therefore favors decomposition. 

 The rock outside the impregnation zone has suffered the most 

 from this, and especially in the sheeted areas has suffered so 

 from oxidation and other changes that it is often impossible to 

 get a definite idea of its original nature. In the mineral druses, 

 where permeable, the waters have deposited a layer of limonite 



