xxxiv GENERAL SUMMARY OF SCIENTIFIC AND 



in many places resting upon these sandstones, which, in their 

 turn, inclose in conglomerate -beds fragments of the older 

 copper-bearing amygdaloids. 



The age of the series of dark-colored sandstones and argil- 

 lites, which carry the silver-lodes of Thunder Bay and its vi- 

 cinity, has been noticed by Dr. Sterry Hunt in a very recent 

 paper, where it is shown that these strata, to which he gives 

 the name of the Animikie group, are overlaid in slight un- 

 conformity by the red and white sandstones and marls of the 

 region, which have been hitherto regarded as the same with 

 those just described as overlying the Keweenaw group. This 

 latter is however wanting in the silver region, where the 

 Animikie group rests directly upon the old crystalline schists 

 of the Huronian, into which also the silver-lodes pass. It 

 would thus seem to be a formation unknown to the south 

 and east of the Thunder Bay region, whose real age and rela- 

 tions can only be fixed by further study. 



The study of the paleozoic rocks in Ohio by Professor 

 Newberry shows clearly that the great movement which 

 gave rise to the so-called Cincinnati axis, along which the 

 Trenton limestone is exposed between the Silurian, Devonian, 

 and Carboniferous rocks found on either side, was not, as has 

 been conjectured by some, simultaneous w 7 ith the movements 

 which have folded these later strata in Pennsylvania, but 

 much earlier. This is shown by the fact that at the base of 

 the Medina sandstone occur beds of a conglomerate made up 

 of the ruins of the older formations, and, moreover, by the 

 fact that the Medina and its overlying formations thin out 

 as they approach, on either side, this central axis, which must 

 thus have been dry land from the time of the Medina forma- 

 tion. This agrees with what we might expect from the phe- 

 nomena seen along the eastern border of the palaeozoic basin, 

 where it is clear, as Hall has shown, that at the same period 

 namely, between the time of the Hudson River group and 

 the Medina sandstone a great stratigraphical and paleon- 

 tological break took place, uplifting the rocks of the Trenton, 

 Utica, and Hudson River groups (which together make up 

 the Cincinnati group of the West). One of the consequences 

 of this movement is shown in the formation of local deposits 

 of conglomerate the Oneida and Shawangunk grits at the 

 base of the Medina; and, as a further result, it is seen that 



