574 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



masses and would have been diverted temporarily from a vertical to a hori- 

 zontal course along the stratification plane of the first sedimentary bed they 

 reached, and that, when this was a comparatively soluble rock like the dolo- 

 mitic limestone of Leadville, they would eat their way gradually into it, 

 either from this surface or from cracks through which they were here and 

 there able to penetrate its mass. A downward current seems, therefore, to 

 best suit the facts thus far observed with regard to the Leadville deposits. 

 It might be objected that a downward current would not necessarily be hot, 

 but it has been found by experiment and observation that metallic minerals 

 may be taken up by cold water, though not so rapidly as by hot. More- 

 over, it is probable that the intrusive bodies retained for a long time suffi- 

 cient heat to sensibly raise the temperature of waters coming in contact with 

 them. 



In looking, then, for the immediate source whence the waters by which 

 these ores were deposited derived their metallic contents, which source 

 should be within a limited distance of the locus of the deposits, since it can- 

 not be supposed that the waters would travel for a great distance through 

 rocks of varying composition without suffering considerable change in the 

 material they held in solution, it would seem natural to consider the rocks 

 in the vicinity of these deposits, and especially those overlying them. 



Metallic contents of country rocks. It was resolved in the early stages of the 

 work to make a careful chemical examination of all the rock varieties of the 

 region, as far as circumstances would admit, selecting comparatively unal- 

 tered rocks, which might be supposed to retain most of their metallic con- 

 tents, and those sufficiently removed from any known ore channels to be 

 free from the suspicion of having received these contents from the waters 

 exuding from such channels. 



This investigation was undertaken solely for the purpose of obtaining 

 facts which might explain the condition of things existing in the region, 

 and was conducted without the bias of any preconceived general theory. 

 Indeed, in the opinion of the writer, our knowledge of the ore deposits of 

 the world is still too limited and superficial to admit of the formulating of 

 any generally and universally applicable theory. On the other hand, the 

 weight of what may be considered actual evidence, as distinguished from 



