THE HURONIAN SERIES 11 



column is absent. Where the Animikie ocairs in districts which show 

 the next underlying series, the Middle Huronian, there is no evidence 

 that the unconformity at the base of the Animikie is any greater than 

 that between the Middle and Lower Huronian or between the Animikie 

 and the Keweenawan. Doubtless the different inter-Huronian uncon- 

 formities do represent variable lapses of time, but we have no data from 

 which we can determine which unconformity is greater than the others. 

 So far as the evidence goes, the unconformity between the Animikie and 

 tlie Middle Huronian is certainly not nearly so important as that between 

 tlie Lower Huronian and the Keewatin. 



In the Marquette and Penokee districts the contrasts, from every point 

 of view, between the Keewatin and Lower Huronian are amazing. The 

 schistosity of the Keewatin existed before the Lower Huronian and abuts 

 at right angles against the sedimentary beds of the latter series. In con- 

 trast with this, the unconformities within the Huronian series, including 

 that at the base of the Animikie, are like other moderate unconformities 

 in sedimentary series. I think no one who has studied the facts in the 

 field where the full succession from the Animikie downward occurs can 

 arrive at any other conclusion tlian that the unconformity between the 

 lower Huronian and the Keewatin is the greatest of the Lake Superior 

 region (see j^ages 12-13). 



On one point in reference to the Lake Superior structure there has been 

 no controversy. This is the relation of the' Keweenawan and Huronian. 

 As already seen, Logan recognized that this series is at a higher horizon 

 than the Huronian. Brooks' studies of the relations of the Huronian 

 and the Keweenawan on the south shore of lake Superior led him to the 

 belief that there is an unconformity between the two. Irving found evi- 

 dence of this unconformity upon the north shore of lake Superior. My 

 own later studies in the Penokee district show that this unconformity, 

 which there is between the Keweenawan and Upper Huronian (Ani- 

 mikie), is one of very considerable magnitude, the differential erosion 

 represented by it amounting to thousands of feet. Studies by W. N. 

 Smith, Clements, and myself in northeastern Minnesota and Canada have 

 still further emphasized the importance of the unconformity between the 

 Keweenawan and Animikie, although here the amount of erosion is not 

 so great as in the Penokee district. 



x\ll who have made extensive studies in the Lake Superior region, with 

 the exception of the later Michigan geologists, have agreed that all the 

 series yet considered, from the Keewatin to the Keweenawan, inclusive, 

 are unconformal)ly below the Upper Cambrian sandstone. Moreover, 

 thoy hold tliat the nature of this unconformity is such as to make it 



