222 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



As in the two former comparisons, the difference in the titanium determined 

 accounts for most of the difference between the totals of these analyses. 



In this case the bases have been more plainly affected than in the first two. 

 The most noticeable change is, as before (in rock No. 2), the abstraction of lime, 

 whicli seems to have been carried farther than in rock No. 2. Yet in this case 

 the loss has not been compensated for by the deposition of magnesia which has 

 itself been abstracted, though not in so great degree so that the combined amount 

 of lime and magnesia in rock No. 3 is less than half what it is in the average 

 type. Simila-ly the alkalies have been extracted; the potash more than the soda. 

 The iron has become more oxidized, but its bulk remains the same. The proportion 

 of alumina has slightly increased, perhaps owing to the loss of weight of the rock, 

 caused by the removal of more material than was brought to replace it. In all, 

 the percentages of lime, magnesia, and the alkalies are 5.57 less in this rock than 

 in the average fresh type. There is also less silica, but the difference in percentage 

 is by no means so great as it was in rocks No. 1 and No. 2, being only 1.71. 

 In the Tonopah rock (No. 3) the percentage of water is 4.64 greater than in the 

 average type, carbonic acid is absent, and there is a very small amount of iron 

 sulphide. In this case, therefore, the gain in water, carbonic acid, etc., is by no 

 means offset by the loss of silica. The chief loss is plainly lime, magnesia, and 

 the alkalies, more particularly lime and next to that potash. In this case the 

 waters have extracted silica to a very slight extent only, and were therefore 

 solutions whose silica capacity was more nearly satisfied than in the case of rocks 

 1 and 2. The tendency to dissolve and carry away lime displayed in No. 2 was 

 more vigorous in this rock, and the same action was displayed in regard to magnesia 

 and the alkalies. 



