APPENDIX—GEOLOGICAL SURVEY. 
425 
be converted into steam or elastic vapor, whose mechanical 
power and properties we understand. 
During the early formation of these stratified rocks—say for 
instance the Potsdam sandstone—the resistance would be 
comparatively small; vent would be easily found through the 
loosely accumulating sand. But as layer after layer was 
added, and the more compact limestone began to form and 
harden above it, resistance would increase, until, to overcome 
it, a general lifting of the strata would take place, by which 
escape would be effected through fissures in the rock along 
the line of those original faults in the plutonic rocks below. 
These fissures in the newly formed aqueous rocks we must 
regard as the result of the same mechanical force acting upon 
the strata from below, hence their conformity to directive 
influences hidden from our view. 
When we take into consideration the great antiquity of the 
lower stratum of the lead district, and that it commenced at the 
closing of the azoic period when the temperature was sup¬ 
posed to be too high to admit of organic existence, and that 
its vast fissures were even then the outlets of radiant heat, 
<8 
nothing is more reasonable than to suppose, that for untold 
ages the strata above these foci of mechanical power, would 
be traversed by heated waters, forced by elastic pressure from 
below through every crack and fissure in th$ rock. This 
water would sometimes find its way through vertical fissures, 
at other time3 between the thin beds of the strata, seeking, as 
such power will always do, those places that give the least 
resistance, and bringing up doubtless at the same time in 
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solution from depths unknown to us, the elements of that 
material that formed our ores. Chemical as well as mechan¬ 
ical activity and force would also be conspicuous and powerful 
along these lines. The solvent power of heated water, aided 
as it would be by material held in solution at various degrees 
of temperature, would become of itself a chemical agency of 
great force, and the result would be chemical action and 
reaction along its course. 
What I would notice here especially is, that physical con- 
