QUEBEC GROUP OF ROCKS, ETC. 45 
ered older. I am not prepared to say that the Potsdam deposit in its 
typical form of a sandstone is anywhere largely developed above these 
shales, where the shales are in greatest force. Neither am I prepared 
to assert its absence, as there are in some places masses of granular 
quartzite not far removed from the magnesian rocks of the Quebec 
group, which require farther investigation; but, from finding wind- 
mark and ripple mark on closely succeeding layers of the Potsdam 
sandstone where it rests immediately upon the Laurentian series, we 
know that this arenaceous portion of the formation must have been 
deposited immediately contiguous to the coast of the ancient Silurian 
sea, where part of it was even exposed at the ebb of tide. Out in 
deep water the deposit may have been a black partially calcareous 
mud, such as would give the shales and limestcnes which come from 
beneath the Quebec group. 
In Canada no fossils have yet been found in these shales, but the 
shales resemble those in which Olent have been found in Georgia 
(Vermont). These shales appear to be interposed between eastward 
dipping rocks equivalent to the magnesian strata of the Quebec group, 
and they may be brought up by an overlapping anticlinal or dislocation. 
We are thus led to believe that these shales and limestones, which may 
be subordinate to the Potsdam formation, will represent the true 
primordial zone in Canada. 
Mr. Murray has this season ascertained that the lowest rock that is 
well characterized by its fossils in the neighbourhood of Sault Ste. 
Marie, near Lake Superior, really belongs to the Birdseye and Black 
River group, and that it rests on the sandstones of Ste. Marie and 
Lacloche, the fossiliferous beds at the latter place being tinged with 
the red colour of the sandstone immediately below them. These 
underlying Lake Superior rocks may thus be Chazy, Calciferous, and 
Potsdam, and may be equivalent to the Quebec group and the black 
colored shales beneath. The Lake Superior group is the upper cop- 
per-bearing series of that region, and rests uncomformably upon the 
lower copper-bearing series, which is the Huronian system. The 
upper copper-bearing series holds nearly all the metals, including gold, 
and so does the Quebec group, each making an important metalliferous 
region, Each when unmetamorphosed holds a vast collection of red 
colored strata. The want of fossils in the Lake Superior group makes 
it difficult to draw lines of division, but if any part represents the 
primordial zone, I should hazard the conjecture that it is the dark 
coloured slates of Kamanistiquia, which underlie all the red rocks. 
