170 KANSAS CITY REVIEW OF SCIENCE. 
amount of iron sulphide, in others very little; while the ratio of gold to silver 
Is inconstant, and the aggregate of both varies from nothing to several hundred 
dollars to the ton. The ores of Eureka run high in lead, contain much iron, 
and about seventy dollars in the precious metals, half gold. half silver. The 
ores of the Emma mine carried less iron, more lead, much more silver, less gold; 
and a little copper; while those of the Cave mine, at Frisco, contain no lead, 
much iron, a little copper, and are sometimes exceedingly rich in both silver and 
gold. In all the chamber.mines yet worked in this country, the ore taken out 
is thoroughly oxidized ; but in the deeper workings of some neighboring fissure- 
veins, the soft, ochery ores of the chambers are found changed below into com- 
pact masses of galena and iron pyrites; the galena carrying the silver—the 
pyrites, the gold. Hence we may conclude that the ore originally deposited in 
the caves consisted of sulphides, and that, whenever these 1nines shall be worked 
below the water-level, ore of this character will be found. It should be said, 
however, that if the theory I have suggested of the formation of the limestone 
galleries and chambers is true, they will not be found to extend to so great a 
depth as the ore-bodies of fissure-veins, since the excavation of the limestone, if 
produced by atmospheric water, must be confined to the zone traversed by 
surface drainage. In a very dry and broken country, the line of permanent 
water-level may be very deep, as at Eureka, where the ore-bodies extend and are 
oxidized to a depth of at least 1400 feet. Such a condition of things could only 
exist in a very dry climate; but we have evidence that there have been great 
climatic changes in our western mining districts; according to King and Gilbert, 
two wet periods having been succeeded by two dry ones, the last prevailing now. 
We may therefore find chambers wrought in the limestone in a dry period below 
the present or normal water-level. The enormous production of gold and silver 
from the chamber-mines already worked proves the great importance and value 
of this class of deposits; and while we may predict that they will be found to be 
more superficial than true fissure-veins, no limit can be fixed to the future yield 
of mines of this character, even though they should not be profitably worked 
below 1500 feet from the surface. 
( Zo be continued.) 
GENESIS AND MODERN THOUGHT. 
BY PRINCIPAL J. W. DAWSON, LL. D., MCGILL COLLEGE, MONTREAL. 
Every age of the word has its own mental habits, part of which are transient, 
passing away with the time that gave them birth; part are permanent, and are 
handed down to succeeding ages. It thus happens that every great permanent 
monument in the world, be it a mountain, a pyramid, or a divinely inspired book, 
is regarded with somewhat different eyes by the successive generations of men. 
he Book of Genesis is such a monument, reaching unchanged from the 
