74 [APPENDIX 



been closely investigated, and in several of the mines the workings have 

 been carried entirely through this rock, and contrary to the anticipations 

 of the incredulous, the setts have not been thrown at -the point of contact 

 with the inferior rocks. Thus far the depth of the granite series has 

 not been found to exceed a depth of but little more than one hundred 

 feet, and in almost every case where shafts have been driven, either on 

 the vein or beside it, the rock has been found in a highly decomposed 

 state, thus presenting but little difficulty in passing through it. There 

 are, in some localities, many small veins running out at different angles 

 from the principal " setts," into the surrounding granite, and when thus 

 appearing in the inverting rocks, marks of dislocation are observable. 

 These interesting features define most clearly the energy and extent of 

 the supporting and injecting forces from below, at the date of the intru 

 sion of the veins, and the angles which the small cross-courses make 

 with the main "setts" from which they emanate, shows most conclusively 

 that the fracture o the superincumbent rocks must have been extensive. 

 Another and a striking feature is also to be observed in this particular, 

 which is, that the small threads found in the granite have a greater power 

 whe*n they enter the greenstone below ; thus indicating that the intru 

 sive dikes spent themselves principally in the superior granite above. 



The 'entire mass of the granitic rocks in the vicinity of the quartz, is 

 of a loose and incoherent texture, from the surface to the lowest point 

 yet reached, and when brought from the greatest depths 'the same gene 

 ral characteristics are found to prevail throughout. It presents a crumb 

 ling, reddish and purple hue, at times faintly spotted with white, its fels- 

 pathic constituent thus imparting a porphyritic appearance to considera 

 ble quantities. When damp it is somewhat clayey, in the dry state, after 

 exposure to the air, it is easilly crushed in the hand, giving the greasy 

 feeling of some of the talcose minerals. These peculiar features may be 

 best examined in and about the towns of Nevada and Grass Valley ; 

 for here they extend over several miles, and the extent to which mining 

 operations have been carried in these sections, renders an examination 

 of all the different phases that are presented in this class of veins, both 

 easy and convenient. 



Immediately below the granite, the greenstone is found underlying 

 this entire section of country, in every instance in which the granite has 

 been perforated, this rock has been found beneath, and when first met 

 with in descending is much broken up, and the fissures filled with foreign 

 infiltrations from above. The trap rock has a blueish-gray and greenish 

 color, often highly charged with pyrites ; the veins on entering this rock 

 change their color from the deep reddish-brown, which they maintain in 

 the granite above, and the cavities filled with the peroxide of iron which 

 has resulted from the decomposition of the pyrites it originally contained, 

 to a clear, white or semi-translucent mineral, holding considerable quan 

 tities of cubic and rhombic crystals of pyrites, which are more or less 

 auriferous. In some of the trapean rocks arsenical pyrites is met with, 

 but this latter is much more common in the southern districts, and on 

 the forks of the American Eiver. 



In every mine throughout the northern districts, in which the green 

 stone has been reached, the veins have penetrated this rock, and in no one 

 instance thus far is it found that the vein has either been pinched or faulted, 



