390 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
In regard to the nature of these greenstones, it is to be said that they 
are not improbably diabases, no microscopic analyses having been made of 
them, while the descriptions of kinds carrying much red feldspar are 
certainly suggestive of the orthoclastic gabbros of Chapter III of this 
memoir. 
The red granitic rocks mentioned as intrusive are also suggestive of 
the red granitic porphyries and augite-syenites of the Keweenawan. Sim- 
ilar granites or granitic porphyries, according to Norwood and Winchell, are 
found among the Animikie slates of the Thunder Bay country. The rocks 
of Lake Huron, according to Logan’s sections, are bent into gentle folds. 
The whole aspect of the original Huronian, as thus described by Lo- 
gan, is strongly suggestive of the Animikie Group of the North Shore. Both 
series are made chiefly of quartzites and slates, with some limestone and chert 
beds, and with interbedded greenstones, along with intersecting greenstones 
and red rocks. Some of this similarity was seen by Logan, who, however, 
could not have realized how strong it was, since he does not seem to have 
been aware that the Animikie Group was prevailingly quartzitic. However, 
on account of the similarity as he saw it, he maintained’ for many years the 
equivalence of the Lake Huron rocks with the native-copper-bearing rocks 
of Lake Superior. Subsequently this view was abandoned, and since the 
Thunder Bay slates were regarded as merely the downward continuation of 
the copper rocks, these two were now considered as newer than the Huron- 
ian® Yet so striking was the resemblance then made out between some of 
the Animikie beds and those of the original Huronian, that a strip of rocks 
along the north shore of Thunder Bay, which are most plainly part of the 
Animikie slates, was separated from them by Logan and put down as Hu- 
ronian.® : 
With my present knowledge it appears to me very probable that the 
original Huronian of Lake Huron, and the Animikie slates of Thunder Bay, 
and thence southwestward to the Mississippi River, are one and the same 
formation. The Keweenawan rocks, as shown later, are newer than either. 
‘Report of Progress of Geol. Survey of Canada, for 1848, p. 2% 
*See T. S. Hunt in Second Geol. Survey of Pennsylvania. Special Report on Trap Dikes and 
Azoic Rocks of Pennsylvania, Part I, p. 69. 
5Geology of Canada, 1863, p. 63. 
a 
