270 GEOLOCxY OF THE COMSTOOK LODE. 



third of the product of the whole Lodk stands in a vertical position and ex- 

 tends 500 feet from the fissure. Below it large masses of diorite are embed- 

 ded in indeterminable vein-matter and diabase. 



In the funnel-shaped mass directly under the croppings a notable feature 

 is the variation in the character of the quartz. This is liard and firm where 

 it lies upon the west wall, and so far from it as the general structure indi- 

 cates that the quartz sheets are parallel to the line of the main fissure. 

 I'^ast of the horse, on the other hand, the quartz is in great part crushed to 

 a condition like that of commercial salt. The horse-matter in this portion 

 of the section is also accompanied by heavy clays. The ore near the crop- 

 pings in this region was heavily charged with galena, blende, and pyrite, 

 differing in this respect from the great bonanza in the same vertical plane, 

 and from the principal ore bodies of the Lode. 



The "great bonanza. Tlic bonauza cousistcd of a group of three bodies, one 



of them far larger than the others, and one of very small dimensions. The 

 cross-section under discussion and the longitudinal vertical projection. Atlas- 

 sheet X., give a better idea of the geometrical form and the position of this 

 important group than any description could do.^ It was composed of 

 crushed quartz, including fragments of country-rock, and carried a few 

 h M'd, narrow, vein-like seams of very rich black ores, consisting of ste- 

 phanite and similar minerals, while nearly the whole mass of "sugar-quartz" 

 was impregnated to a moderate extent with argentite and gold, the latter 

 probably in a free state. The immense volume of these soft ores more than 

 compensated for their moderate tenor,- and much the greater part of the 

 entire yield of the bonanza was derived from them. They carried a mod- 

 erate amount of pyrite. A great part of the space stoped out consisted of 

 fragments of country-rock, impregnated, however, with ore, and assaying 

 well. These fragments were highly decomposed, but perfectly recognizable 

 by their green color and traces of porphyritic structure. They were not 

 rounded, and I never saw traces of the concentric structure which any pro- 

 cess of replacement must have impai'ted to them. On the contrar}', they 

 were as sharply defined as if freshly broken. Comb structure was not visible 



'Mr. Church gives excellent illustrations of the form of this body on diflerent levels, but the 

 black rock west of the bonanza is not black dike. 



'^The ore of the great bonanza averaged about $S0 per ton, but this included the rich stringers. 



