- 
the Copper-bearing Rocks of Lake Superior. 325 
remarked, that many of the members, both of the lower and@ 
upper parts of the Quebec group, have by no means the char- 
acters of deep-sea deposits. It has already been stated, that the 
beds of passage between the littoral portions of the Potsdam 
and Calciferous formations, suggest the opinion, that, towards 
the termination of the Potsdam era, a ual sinking of the 
surface had occurred. In order to obtain the conditions for the 
accumulation of the coarser sediments, which commence near 
the base of the Quebec group, it must be supposed, that, shortly 
after the beginning of the Calciferous period, a great continental 
elevation occurred ; carrying the littoral deposits of the Potsdam, 
and the beds of passage just mentioned, high above the sea, and 
inging the area at the base of the Quebec group comparatively 
hear the surface. The successive coarse deposits of the group 
Indicate a subsequent gradual subsidence, at unequal intervals, 
Probably with subordinate oscillations, until the early shallow- 
Water strata were again submerged; to be first partially covered 
over by deposits of the Chazy formation, and then, almost uni- 
versally, by those of the Trenton and Hudson groups. 
In this way may be explained the break which occurs in the 
Succession of life between the Calciferous and Chazy, in the shal- 
low-water deposits of these formations between the Allumettes 
Islands and Montreal, as well as among the Mingan Islands, 
he interruption in the succession of deposits between the base 
of the Trenton group and the Potsdam, at St. Ambroise; and 
that between the same base and the Laurentian, from the north 
re of Lake Huron to Kingston, as well as in the vicinity of 
hay, is in the same way accounted for. The b in the suc- 
cession of life between the Chazy and the Trenton group, is not 
80 great as that between the Calciferous and the Chazy. It is 
hot yet quite certain, that, at the marginal outcrop of the latter 
formations in Canada, a single species passes upwards into the 
azy; while about one-sixth of the species of the Chazy are 
known to occur in the Birdseye and Black River formation, at 
the base of the Trenton group. It seems to be in accordance 
with this, that we have evidence of a somewhat sudden submerg- 
happens that the surface on which these beds rest, is rough, an 
into sharp projecting ledges and deep fissures, wh 
filled up and covered over by the deposits in ee, 
Sufficient time had elapsed to pern to 
Worn down. Instances in illustration of this occur on the Snake 
Islands, west of Lacloche, in Lake Huron, where the Birdseye 
