7i6 C. K. LEITH AND R. C. ALLEN 



Middle Huronian (Animikie) of these districts is the general 

 prevalence of intrusive granite. Heretofore these granites have 

 been variously correlated, from Laurentian in the Gogebic, northern 

 Wisconsin, and Menominee districts through the Upper Huronian 

 in the Crystal Falls district to Keweenawan in the Florence- 

 Menominee and northeastern Wisconsin areas. 



In the Menominee district Bayley found that the granite south 

 of the Menominee River intrudes a series of basic volcanics called 

 the Quinnesec schist, which he correlated with the Keewatin. 

 Although it was realized that the correlation of the Quinnesec 

 schist as Keewatin introduced a conception of structure quite 

 out of accord with natural inferences on the basis of the facts, it 

 remained for Corey and Bowen, working under the direction of 

 Van Hise and Leith in 1905,^ and Hotchkiss in 1910,^ to show con- 

 clusively that the Quinnesec schist is partly intrusive into, but in 

 greater part interbedded with, the upper part of the Upper Huro- 

 nian, i.e., Animikie.3 



Inasmuch as the granite was thus proven to be the youngest 

 rock in these districts, and the youngest pre-Cambrian sediments 

 had been correlated with the Upper Huronian, Leith and Van Hise 

 in 191 1^ correlated the granite with the Keweenawan and extended 

 the boundaries south and east to include several thousand square 

 miles of acid intrusives in north-central Wisconsin which had been 

 mapped and described by Weidman in 1905.^ 



It is interesting to note here that Brooks and Wright had cor- 

 rectly interpreted these relations as early as 1876, although they 

 did not, at that time at least, comprehend the extent of the great 

 mass of intrusive granite. To quote from Brooks: 



In the summer of 1874 Chas. E. Wright and myself, exploring the country 

 west and south of the Menominee River about 90 miles from its mouth, under 

 the auspices of the Wisconsin Geological Survey, observed a large granite 



' Unpublished notes of field work done in 1905 by G. W. Corey and C. F. Bowen. 



^ Unpublished field notes of W. O. Hotchkiss. 



3 Middle Huronian of this article. 



^ Monograph 52, U.S. Geol. Survey. 



s S. Weidman, "The Geology of North Central Wisconsin," Btill. Wis. Geol. and 

 Nat. Hist. Survey, No. 16, 1907. 



