GRENVILLE SERIES OF EASTERN NORTH AMERICA 635 



ings series" is the less altered phase of both and to employ it now, to 

 designate either, is to use it in a new sense differing from that of 

 Logan and thereby introduce confusion in the nomenclature. Messrs. 

 Miller and Knight conjecturally set down the lower of these two 

 series, with its enormous body of limestone and other sediments, 

 as Keewatin and as the equivalent to the Keewatin iron formation of 

 Lake Superior, correlating the upper series with the Huronian. 



Van Hise in his recent "Presidential Address,"^ however, very 

 properly declines to accept this view until some evidence has been 

 adduced in favor of such a supposition. 



In fact, if conjecture must be indulged in, it is much more reason- 

 able to correlate the whole series, being, as it is, essentially a great 

 sedimentary limestone series, with the Huronian, owing to the fact 

 that as we come east in the Huronian developments of the iron ranges 

 of Lake Superior, limestones become more abundant. The thickest 

 and greatest bodies of limestone in the whole western pre-Cambrian 

 are those of the Menominee Range. It may easily be that still further 

 east the Huronian becomes still more highly calcareous and takes 

 on essentially a limestone facies, while the Keewatin has essentially 

 a pyroclastic development. 



But it must be borne in mind that so far as is known at present, the 

 Grenville series may be a distinct entity, separate from either and 

 differing in age from both. This can only be ascertained by a further 

 detailed examination of the intervening areas. 



Whatever may be the result of future studies — whether it be 

 established that the Grenville series is to be correlated with members 

 of the pre-Cambrian development in the west or whether it proves to 

 be a series differing in age from any of these — it remains the greatest 

 development of limestone known in the pre-Cambrian of North 

 America and one of the greatest limestone developments of any age. 



I Bull. Geol. Soc. of America, March 30, 1908. 



