R. D. Irving — Is there a Huronian Group t 249 



Art. XXVIII. — Is there a Huronian Group ? by R. D. Irving. 



[Continued from page 216 of last number.] 



TV. Deciding that the type Huronian is a true group is 

 a very different matter from concluding that all rocks which 

 have been called Huronian in other regions are the geological 

 equivalents of the type series. On the contrary, even in the 

 Lake Superior region, and by members of the Canadian Sur- 

 vey itself, there have been referred to the Huronian most di 

 verse formations. Some of these seem properly enough so 

 referable ; others as surely are not so referable, while as to 

 the reference of still others there must remain very much 

 doubt. A discussion of those correlations which have been 

 attempted between the type Huronian and the rocks of distant 

 and always disconnected geological basins would be of little 

 utility. Unsupported lithological evidence only is available 

 for such correlations, and, in point of fact, with most, if not all 

 of those who have attempted these distant correlations there 

 has prevailed a most singular misapprehension as to the real 

 nature of the type or original series. For this misconception 

 Dr. T. S. Hunt seems to be mainly responsible, he having 

 steadily represented the type series to be a truly crystalline 

 one, and as composed of highly folded crystalline schists, 

 mainly chloritic slates and schists.* Yet there is no such series 

 of rocks in the original or type area, whatever may be true of 

 other regions whose rocks have been called Huronian. 



Not to concern myself then with these distant correlations, 

 in which I am able to feel but little confidence, I wish next 

 to consider briefly how far the rocks of other districts in the 

 region of Lakes Huron and Superior may be correlated with 

 the type Huronian. 



For the establishment of such correlations we have of course 

 no fossils, and must depend on the lithological characters and 

 subordinate stratigraphy of the rocks whose reference to the 

 type series is to be discussed, as also on their structural rela- 

 tions to adjoining rock groups. There is good reason to 

 believe that in the region which stretches from the north shore 

 of Lake Huron to the Mississippi River we are dealing with 

 one geological basin, so far as the rocks which I take to be the 

 equivalents of the type Huronian are concerned ; in other 



* " A great series of chloritic slates and conglomerates with, interstratified 

 greenstones, quartzites and limestones," Azoic Rocks, p. 70 ; " group of chlo- 

 ritic slates with greenstones and quartzites," ib. p. 72 ; "the younger and uncon- 

 formable series of crystalline rocks found on the shores of Lake Huron," ib. p. 

 72; "the contrast between the highly disturbed condition of the former 

 [Huronian] and the broad folds and gentle dips of the Montalban," ib. p. 215. 



