10 C. R. VAN HISE THE PROBLEM OF THE PRE-CAMBRIAN 



ically as are any other sedimentary formations. Thus in all essential 

 respects they found this series to be like the original Huronian of the 

 north shore of lake Huron, and they therefore gave the group this name. 

 Later the work of Irving and myself showed that there was an uncon- 

 formity between the basement complex and the Huronian. My later 

 work led me to the division of the Huronian into two unconformable 

 series, which were called Lower Huronian and Upper Huronian. Still 

 later work by Seaman showed that my Lower Huronian is divisible into 

 two unconformable series, and thus it follows that on the south shore of 

 lake Superior, as on the north shore of lake Huron, there are three un- 

 conformable series to which the term Huronian have been applied, and 

 which may be called Lower, Middle, and LTpper. 



The upper of these series is the so-called Animikie. If it were prac- 

 ticable to generally separate this series from the two lower, this would be 

 most advantageous; for in that case the upper Huronian would have a 

 distinctive name, and the term Huronian could be restricted to the latter 

 two. This would be a great gain in the matter of clearness of nomen- 

 clature, and also this usage would give the term Huronian a scope almost 

 exactly equivalent to its usage as first applied on the detailed maps of 

 Logan and Murray in the area immediately adjacent to lake Huron. But 

 as yet it has not been practicable to separate the Animikie from the other 

 divisions of the Huronian over broad areas, and therefore apparently for 

 the present the latter term must be continued to cover all three series, 

 allowing the term Animike to be used for the upper series where it can be 

 discriminated. 



In this connection it may be mentioned in passing that the break be- 

 tween the Animikie and the Keewatin, wliich has been recognized from 

 the first, Lawson emphasizes as the greatest which obtains in the Lake 

 Superior region. In various localities the Animikie rests directly on the 

 Lower Huronian or the Keewatin, and the Middle or both the j\Iiddle 

 and Lower Huronian are therefore absent. In the former case the un- 

 conformity at the base of the Animikie represents two unconformities 

 and the intervening series. In the latter case the unconformity at the 

 base of the Animikie represents three unconformities and tlie two inter- 

 vening series. In this case the unconformit)'' corresponds to a greater 

 interval of time than can possibly be represented by the unconformity be- 

 tween the Lower Huronian and the Keewatin, because such unconformity 

 includes this unconformity and also two others with their intervening 

 series. 



However, a geological classification must be made on the basis of a full 

 succession rather than on the basis of a succession in which a part of the 



