370 S. D. Irving — Is there a Huronian Group f 



been seen that we can take only the latter. It has also already 

 been abundantly shown that the second, third and fourth 

 requirements are fully met in the case of the Huronian. As 

 to the fifth, it is to be said that a thickness of 18,000 feet of 

 sedimentary strata, extending, as the Lake Superior Huronian 

 does — or did before erosion — over an area of 800 by 400 miles, 

 and in all probability over an area as large again as this, cer- 

 tainly has " presumptively " its exact chronological equivalent 

 in other geological basins. That it has been recognized in 

 other countries cannot be said. Eocks of fragmental origin 

 which are with sufficient probability, in part at least, the equiva- 

 lents of the type Huronhm have been recognized in different 

 countries, and on different continents, between the Cambrian 

 base and the Archaean schists ; but all that we can now say 

 with regard to them is that they belong to the same general 

 geological interval with the Lake Superior Huronian. As to 

 the sixth or final characteristic, that the group is defined by 

 paleontology, it is to be said that the Huronian is so only so 

 far as it is proved to be pre-Cambrian by the fact that it ante- 

 dates by an immense interval of time rocks holding Cambrian 

 fossils. It has so far yielded no recognizable fauna of its own. 



Thus the only departure from the definition lies in the fact 

 that the Huronian, while plainly in all other respects a group, 

 is not to be correlated with any particular pre-Cambrian or 

 other rocks by a comparison of fossils. The writer himself is 

 not among those who accept paleontological correlations in the 

 extreme way in which they have frequently been presented to 

 us in the books ; indeed, he is disposed to agree with those 

 others who think that, while there has been a general similarity 

 in development in different basins of rock growth, or even in 

 different continents, the similarly named groups of these differ- 

 ent basins and continents have hardly been always so exactly 

 correspondent or even homotaxial as has generally been sup- 

 posed. It would seem that the author of the quotation referred 

 to held also somewhat the same views from the fact that he 

 speaks of the ordinarily accepted groups as arbitrarily deter- 

 mined, in part at least. But, waiving such considerations, it 

 would seem that one need hardly do more than ask the ques- 

 tion — whether the great thickness of rocks in the Huronian 

 series, not to speak of that included within the Keweenawan, 

 is to be ignored in geological chronology merely because its 

 exact geological equivalents in other regions are not strictly 

 recognizable as such — to receive a negative answer. 



The Huronian then is a true sedimentary group in origin, in 

 volume, in chronological distinctness from other groups above 

 and below it. It is not only comparable, as to volume, with the 

 ordinarily recognized rock groups, it exceeds most of them ; 



