700 R. C. ALLEN AND L. P. BARRETT 



Copps group {Post-Animikie) . — -The Copps group is the name 

 which we propose for the rocks occupying the area which is mapped 

 and described in Monograph ig, U.S. Geol. Survey, under the heading 

 "Ferruginous Slates of the Eastern Area." It is composed of a 

 basal conglomerate, overlain by a great thickness of graywacke 

 slate, which is highly ferruginous in the western half of its area 

 and is associated in certain horizons, especially the lower ones, with 

 considerable non-clastic chert and here and there with jasper. 



The important member of this formation for purposes of this 

 article is the basal conglomerate. This conglomerate is exposed in 

 many places and shows a characteristic variation in content of 

 matrix and pebbles with the character of the formation on which 

 it rests. 



From section 23, T. 47 N., R. 43 W., east to the extremity of 

 the range it is in contact with the Presque Isle granite; the con- 

 glomerate here is composed of granite pebbles and bowlders ran- 

 ging up to 4 or 5 feet in diameter imbedded in a matrix of sideritic 

 arkose, the bowlder content exceeding the volume of matrix. A 

 few pebbles of chert, jasper, quartzite, and greenstone appear in a 

 large exposure near the S.W. J of section 24, T. 47 N., R. 43 W., 

 but one mile west of this place, near the old Copps mine, where the 

 Copps formation truncates the Animikie, the granite pebbles have 

 entirely disappeared, giving place to smaller fragments of chert 

 and quartzite, chert predominating, derived from the Ironwood 

 and Pahns formations. The matrix here has increased in relative 

 importance and has changed to finely clastic chert and quartz 

 cemented by iron carbonate. North of the center of section 2 1 and 

 near the N.W. corner of section 19, T. 47 N., R. 43 W., the con- 

 glomerate is exposed in test pits. In these localities the matrix 

 has the character of graywacke in which are inclosed numerous 

 small rounded pebbles of chert, jasper, and vein quartz. The 

 conglomerate has also been penetrated by drilling in section 21, 

 T. 47 N., R. 43 W., and, according to J. M. Louggeor, Jr., occurs 

 ''all along the north and east edges of the greenstone area" in sec- 

 tions 13, 14, 19, and 24, T. 47 N., R. 44 W.^ 



^ A thesis on the geography of part of the Gogebjc Range. Harvard University, 

 1915 (unpublished). 



