70 Lieut. Ruggles on the Copper Mines of Lake Superior. 
stead waves. The superficial portion of the isthmus, close at 
hand, is composed principally of the detritus of conglomerate, 
and as we descend, this rock is disclosed in its characteristic solid- 
ified form. The space thus presented near the landing sinks 
from the beach outward to twenty-five feet water, and lies before 
the eastern channel of the open roadstead—leaving the mind to 
comprehend, involuntarily, that it has been gradually cleared of 
an immense mass of conglomerate and its detritus by the abrading 
waves. Nearly opposite the western roadstead channel, at ¢/, a 
similar impression has been made upon the isthmus. The evi- 
dence of cause and effect is here strikingly exemplified by the 
result, and the conclusion is therefore rational, that a long period 
of repose has elapsed since disturbing forces have left records of 
their power. Nevertheless, I regard the Kewaiwenon peninsula 
as the result of progressive elevating periods, and accordingly 
that most if not all of the mineral veins throughout this region 
have been formed by volcanic or igneous action, under the pres- 
sure of incumbent waters. That the trap was first projected 
through the conglomerate, and that then the mineral veins were 
formed, there can be little doubt... 
I have entered into these details because I regard this region as 
presenting many striking peculiarities, a knowledge of which 
will become of great importance as the mines are progressively 
developed, and which will be found to extend, by practical analo- 
gy, to the whole mining region of the northwest; and I know 
of no method by which to arrive at important and practical gen- 
eralizations in the geology of mining, except by a just apprecia- 
tion of elementary indications and principles. I am not aware 
that any more remarkable instance is found on record where me- 
tallic bowlders, of great richness, density and beauty, have been | 
traced, in a manner so satisfactory, to the parent vein.. The 
question is thus presented, hypothetically, whether the true veins, 
containing copper and its combinations, were formed by subter- 
ranean igneous agency, under the pressure of incumbent water, 
or subjected only to the pressure of the atmosphere ; and the same 
views extend, by analogy, to the lead mines. The question is 
very important as regards the origin of mines, and especially since 
this rich vein appears to have been formed and preserved under 
the pressure of a great body of water,—while disseminated me- 
tallic copper, found in many veins, may possibly indicate that 
