ORIGIN AND CLASSIFICATION OF ORE DEPOSITS. 169 
usually find the sulphides decomposed to a considerable depth; the copper ores 
converted into carbonate and silicate, the sulphide of silver into the chloride. 
Chambers or pockets in limestone form the receptacles of ore in many coun- 
tries; but nowhere else are such striking examples of this class of deposit as 
those found in our Western mining districts. From a study of these, I have been 
led to add them to the catalogue of forms of ore-deposit as a distinct and 
important addition to those given by other writers. The distinctive characters 
of these accumulations of ore in chambers and galleries has not been heretofore 
generally recognized, and a want of information in regard to their true nature 
has led to much litigation and heavy losses in mining. The best examples of 
chamber-mines are the Eureka Consolidated, Richmond, etc., of Eureka, 
Nevada ; the Emma, Flagstaff, Kessler, etc., in little Cottonwood District; and 
the Cave Mine, near Frisco, Utah. All these mines are alike in this, that the 
ore is found more or less completely filling irregular chambers in limestone. 
Some of these ore-bodies are of great size, and the aggregate product of these 
chamber-mines is so great as to make it necessary to record this as one of the 
most important forms of metalliferous deposit. From the Potts chamber in the 
Eureka Consolidated mine, it is said that ore of the value of a million dollars 
was taken, while a still larger amount was produced from the great chamber of 
the Emma. The origin of these chamber-deposits is, in my judgment, simply 
this: A stratum of limestone, more than usually soluble in atmospheric water, 
carrying carbonic acid—which dissolves all limestones—has at some time been 
honey-combed by chambers and galleries such as those which traverse the lime- 
stone plateau of Central Kentucky, of which the Mammoth Cave is an example. 
Subsequently this rock has been broken through and upheaved by the subterra- 
nean forces which have disturbed all our important mining districts; and through 
the fissures then formed mineral solutions ascended, flowing into any receptacle 
opened to them. Where these fissures cut an insoluble rock, they became, when 
filled, simply fissure-veins; but where a cavernous limestone was broken into, 
such caverns and galleries as were opened were more or less filled with ore. It 
has been suggested that the caves now holding ore were excavated by the 
metalliferous solution; but we find some of them entirely empty, with their sides 
incrusted with spar, and having all the characters of ordinary limestone caves, 
and even where the-ore occurs, the walls of the cavity have the same character, 
are hard and unimpregnated with ore. Hence we must conclude that the cham- 
bers were formed, like modern caves, by surface water; and when the country 
was upheaved and the rock shattered, only part of them were opened, and that 
- these received the solution and ore, while the unopened ones remained empty. 
The character of the ore contained in the chambers varies much, as it does in 
the fissure-veins of our mining districts; and the solution from which they were 
filled must have been different in the different localities where they occur. 
Argentiferous galena was evidently the most abundant ore deposited in the 
chambers, as it is elsewhere; but in some cases, this is associated with a large 
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