LAKE SUPERIOR HIGHLANDS: THEIR ORIGIN AND AGE 



CHARLES KEYES 

 Des Moines, Iowa 



The dominant relief feature of the highland region about Lake 

 Superior is an even, distinctly elevated plain in which the rivers are 

 deeply intrenched. The genesis of this broad upland plain is a 

 moot question of long standing. Its settlement involves the deri- 

 vation and facial expression of the landscape over more than one- 

 quarter of the entire North American continent. 



At first glance the possibilities of the present peneplain's dating 

 back in its formation to Early Cambrian, or even to pre-Cambrian, 

 times, as is sometimes argued, seems so remote as almost to pre- 

 clude serious consideration. Only by merest chance could there be 

 survival of any remnant of so ancient a grade-plane. This chance 

 lies in the exhuming of the old peneplain by the slow and uniform 

 removal of a soft Paleozoic covering. Such a facet, if it persisted, 

 would be quite small necessarily, coincidental, and, more properly, 

 a product of some subsequent epoch of planation. Proofs of its 

 antiquity have to be sustained by testimony overwhelmingly per- 

 tinent and convincing. 



Indubitable evidence fixing the age of such a peneplain would 

 not be likely to be found within the area of the highlands itself. It 

 even might not be displayed anywhere within the limits of the great 

 crystalline shield of Canada at a^l. Probabilities are for its dis- 

 closure far outside of the immediate elevated region. It is not a 

 satisfactory solution of the problem to connect such an elevated and 

 dissected plain with one of closely similar attitude emerging from 

 beneath Cambrian sediments. In a continental geologic column 

 there are many old plains — some only of provincial extent, but many 

 of continental span or of dimensions as wide as such plains ever 

 attain. To some place beyond the margins of the highland flats 

 must attention first be turned for testimony bearing upon their age. 



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