288 GEOLOGY OF THE COMSTOCK LODE. 



from above, as was the case with that body. The want of indications of 

 such an opening from above is due simply to the fact that from the nature 

 of the case the accompanying subsidiary phenomena are on lower levels than 

 the opening. At least one other type of opening may occur, which is as 

 likely to carry ore as those just mentioned. Where large bodies of rock 

 are broken and dislocated, interstitial spaces of considerable size may readily 

 form within the mass. An enormous volume of such material exists in the 

 lower levels of the north end mines, and nothing would be less surprising 

 than the discovery of one or more ore bodies in that locality. Attendant 

 upon the ore bodies and somewhat below them to the east, the hanging wall 

 will probably be more heavily charged with pyrite than the average rock 

 of the east country, as has been the case with former bonanzas. 



Of the actual precipitation of ore and gangue from solution little is 

 known. It is very natural to connect it with surface influences, and hence 

 to suppose that ore must be limited to certain deptlis. Such an hypothesis 

 is frequently held by mining men, but experience does not confirm it ; for 

 though there are shallow deposits, there are many deep ones. The gold 

 veins of California and Australia show no tendency to give ovxt in depth, 

 when affected by no other unfavorable conditions, such as a change of rock; 

 and the mines of Pribram, in Bohemia (the only ones, I believe, which are 

 deeper than those on the Comstock), were never so rich and profitable as 

 they have been since the 3,000-foot level was passed. 



The western limit of the diabase is the only ground in which impor- 

 tant ore bodies ever have been or are ever likely to be found in the Com- 

 STOPK mines, and exploration should, in my judgment, be confined to the 

 neighborhood of this contact. Money spent elsewhere will almost certainly 

 be wasted. As long as the east country continues to show an extensive body 

 of diabase, there is no reason for discouragement. Should tliis rock ever nar- 

 I'ow to a mere dike between diorite walls, the outlook would be gloomy; 

 but it is highly probable that such a change occurs, if at all, only at a 

 point far below the limit which technical difficulties will set to exploration. 



The whole contact between diabase and the underlying rocks is worthy 

 of careful exploration. Evidences of disturbance and decomposition are to 

 be regarded as indications of the possible neighborhood of ore, and regions 



