THE LODE. 271 



in the bonanza on a large scale, but where masses of country -rock were 

 favorably placed, the space between them often showed this peculiarit}-, 

 indicating- that the fragments had acted as centers of crystallization for the 

 (puirtz. The same appearance was noticed by Mr. King in the earlier 

 bonanzas. Clays were by no means a prominent feature of this body, 

 though not absent. The endless sheets of clay following and intersecting 

 the ore bodies which were so striking in the upper levels throughout the 

 Lode seem to have disappeared below the junction of the fissures. To the 

 east of the bonanza, especially in the region exposed by the north branch 

 of the Sutro Tunnel, the rock is very heavily charged with pyrite, as well 

 as greatly decomposed; and the sulphuret is clearly formed within the 

 auo-ite crystals of the diabase. The dioritic masses east of and below the 

 bonanza are shattered and somewhat decomposed, but not to tlie same 

 extent as the augitic rock The material laid down as " vein-matter" on this 

 and the other sections is crushed rock, so highly altered that its original 

 character cannot be determined with certainty. The color underlying the 

 conventional markings which designate vein-matter indicates what, in my 

 opinion, is its probable lithological origin. 



Inferences from the c. & c. section.— It is SO dlfficult to rctalu detailed dcscriptions 

 in the memory, that it seems advisable, in the interest of the reader, to draw 

 such inferences from each section as are justifiable, without waiting till they 

 have all been passed in review. The occurrence of the secondary fissures 

 on the CoMSTOCK appeared to Baron v. Richthofen clear evidence that the 

 surface had not undergone great erosion since the formation of the vein. Mr. 

 King concurred in this opinion, and it also appears to me essentially a sur- 

 face phenomenon ; for had the east wall near the present top of the fissure 

 been backed up by thousands of feet of rock, it is difficult to see how it 

 could possibly have yielded in the manner shown by the section. The 

 secondary fissures must, too, have been caused by faulting action, for in no 

 other way can a tendency to rupture in a vertical direction be accounted 

 for. That the east country throughout the mines, and prominently in this 

 neighborhood, shows numerous signs of faulting, has already been explained 

 at length, as well as that the sheeted structure is not ascribable to eruptive 

 bedding. 



