476 Correspondence, 



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 limestones 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 Oleni 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 color of the sandstone immediately below them. 

 These underlying Lake Superior rocks may thus be Chazy, Calcife- 

 rous, and Potsdam, and may be equivalent to the Quebec group and 

 the black colored shales beneath. The Lake Superior group is the 

 upper copper-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, includ- 

 ing 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 con- 

 jecture that it is the dark colored slates of Kamanistiquia, which 

 underlie all the red rocks. 



Professor Emmons has long maintained, on evidence that has 

 been much disputed, that rocks in Vermont, which in June 1859 

 I for the first time saw and recognized as equivalent to the mag- 

 nesian part of the Quebec group, are older than the Birdseye 

 formation ; the fossils which have this year been obtained at Que- 

 bec pretty clearly demonstrate that in this he is right. It is at the 

 same time satisfactory to find that the view which Mr. EiUings 



