Lieut. Ruggles on the Copper Mines of Lake Superior. 67 
The point ois distant about forty yards from g, and at o the vein 
of black oxide rises within two feet of the surface, through well- 
defined walls of conglomerate rock, near the crest of an elevation 
of eight feet above the crop of the new red sandstone. The 
latter rock dips some degrees towards the harbor, and rests upon, 
at its outcrop, most probably, a trap dyke, running parallel with 
the small lake. The metallic bowlders were found at m, in a 
stratum of drift, consisting of coarse gravel intermixed with a va- 
riety of pebbles and bowlders, presenting the characteristics of a 
well-worn shingle beach. During the progress of discovery, the 
first question was, whether these metallic bowlders were genuine 
drift, in their present distinct masses, or an accidental deposit 
from an iceberg,* subsequently broken into fragmgnts ; or, indeed, 
of local and isolated formation. Their number, density, and uni- 
form composition, together with evident marks of attrition and 
abrasion in the characteristic stratum in which they were found, 
left no doubt in my mind that they were genuine drift; and 
accordingly, keeping in view their clustered position and density, 
that they were, at a remote period, driven from a vein of identical 
composition. This naturally led to the examination of a faint 
undulation, near the crest of the elevation close at hand; which 
proved to be a crevice in which the vein was subsequently found, 
and in which a space of some twenty feet, filled with detritus 
containing occasional bowlders of ore, confirmed my previous con- 
victions, that it was from this crevice the whole mass of metallic 
bowlders had once been driven. 
Another enquiry necessarily follows, viz. to what agency must 
the translation of these bowlders be attributed, and did the united 
agency of present causes produce these results? It has been 
already remarked, that the bowlders were found about ten feet 
above the present surface waters of the lake, and that the vein 
lies in the slight elevation some eight or ten feet above the bowl- 
ders. It is to be observed, that the vein ranges, under a small 
angle with a perpendicular, to the longitudinal axis of the lake 
and the direction of the subterranean dyke; consequently, some 
of the heaviest bowlders must have been transported fifty or sixty 
feet, and almost all nearly that distance, over the crop of the new 
red sandstone. These masses have a density approximating 
* This, also, would be comprehended under the general scope of drift.—Eps. 
