96 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



never accumulates in any considerable quantity on the floors, but the 

 atmosphere is always damp. The growth of aragonite crystals is not con- 

 fined to the roofs and sides of the caves, bowlders which have fallen from 

 the roof often being covered with them. Whether these crystals are of 

 stalagmitic origin or whether they owe their formation to exudations from 

 the floor is uncertain, but the latter supposition seems the more likely, for 

 although drops of water were seen falling from clusters of aragonite crys- 

 tals in the roof no corresponding aggregations were noticed where the drops 

 struck below. The caves above ore bodies do not differ in any respect from 

 those in which no ore is found, and although they may have been formed 

 at a different period there is no reason to suppose that they owe their origin 

 to a different cause. 



connection of caves with the outer air. — That some of these caves are connected 

 together by openings, and that they have connection with the outer air, is 

 proved by the fact that in many of them there is a very decided draught 

 of air, although they may be several hundred feet below the surface. In 

 some instances this draught is so strong that a lighted candle held near 

 contracted openings leading to the caves is extinguished. 



Depth to which the cave formation extends. — From the foregoing, it appears that 

 the cave formation in general does not extend to any very considerable 

 depth and that its limit in Eureka is probably reached within a thousand 

 feet. If the theory of a simple crystallization of minerals from solutions 

 in pre-existing caves were correct, it is evident that the practical limit of 

 ore deposition would be reached at the point where cave formation was no 

 longer possible. This would naturally be the point where the carbonic 

 acid solution, being saturated, ceased to dissolve limestone. In Eureka, 

 the limit of the cave formation is probably reached in less than a thousand 

 feet, or before the water level" is attained, as in the Richmond ground 

 between the 7th and 9th levels there are several partially open fissures 

 which, although they show that considerable water has passed through 

 them, nevertheless do not exhibit anything like the same amount of corro- 

 sive action which is everywhere apparent in the upper caves. The struct- 



" In speaking of the water level, reference is had to the mines of Euby Hill, those of Prospect 

 Mountain not yet having reached that depth. 



