GEOLOGY OF LAKE SUPERIOR. 119 
—similar to those which form the Laurentian strata beneath them, with others, however, 
not recognized as from any known Laurentian sources. Bands of limestone and dolomite, 
more or less crystalline, are found in both Laurentian and Huronian areas and, if we 
except the disputed organic form Eozoün, no fossil whatever. 
Logan, as I have elsewhere pointed out, never affirmed this unconformity ; and, in 
the Geology of Canada, 1863, he very significantly designated the Laurentian a system, 
while he called the Huronian a series, and described it as “following,” not resting uncon- 
formably on, the Laurentian. In prosecuting the geological survey in Eastern Canada, it 
has been found impossible, after much close and careful examination, to define or even to 
recognize any constant and reliable line of demarkation by which to separate the great 
series of crystalline strata which underlie the lowest Cambrian formations, and they have 
consequently been there grouped together and described as Pre-Cambrian. A similar 
difficulty has, I understand, been encountered in the Pennsylvania Survey, and also in 
Treland, while in the Western States, no where could any division be established in the 
Archean crystalline formations, either by King, Powell or Wheeler. 
It is probably in the region north and north-west of Lake Superior that the ques- 
tion will ultimately be settled. But, in the mean time, our final judgment on it, so far as 
Canada is concerned, had better be deferred, pending a further and more extended examina- 
tion of the region referred to, which is now being made accessible by the construction of 
the Canada Pacific Railway through it. 
As regards the second question I have referred to, Professor Irving, quite recently, 
(Science No. 13, May 4, 1883) says: “ I am confident that, with the evidence that I now have 
in his hands, Mr.Selwyn would at least think the matter worth looking into.” This refers 
especially to the supposed identity of the Huronian and the Animikie, and is certainly 
correct, as, whether I have the evidence spoken of in hand or not, I propose during the 
coming summer to further investigate this question. But there seems no reason why very 
great unconformities should not exist in an area between two formations which elsewhere 
follow each other without any apparent break; and if the Animikie black shales and 
dolomites represent, as I hold they do, some part of the great Lower Cambrian system 
(Acadian or Primordial), then that they should in some part of their distribution apparently 
pass downward without unconformity into folded Huronian schists, or even appear to 
dip under the latter, would only be a repetition of what seems, indeed is proved, to occur 
in the Appalachian region. Professor Irving is mistaken in supposing (Science, No. 13) 
that I have not seen the typical Huronian of the north shore of Lake Huron. I have seen 
it at several points, and I have studied and examined very large collections from it, and 
compared them with others from the supposed Huronian belt immediately in rear of 
Thunder Bay, which I have also examined on the ground ; and I can say that, physically 
and lithologically, they very closely resemble each other and, as I have elsewhere stated, 
also large portions of the so-called altered Quebec Group, while they essentially differ in 
both these respects from the Animikie black shales, cherts and dolomites which abut in an 
almost horizontal attitude against the Thunder Bay Huronian, in such a manner that no 
one would, I think, hesitate for a moment on the question of their entire unconformity, as 
stated by Logan, Geology of Canada, 1863, p. 67. 
Whether the iron-bearing rocks and schists of Vermilion Lake are really Huronian 
