BASEMENT COMPLEX OF STURGEON" EIVEE TONGUE. 463 



ones — i. e., Menominee (Hurouiau) — while the granites and schists belong 

 to the Basement Complex on which the Lower Algonkian beds tliroughout 

 Michigan have been laid down. 



THE BASEMENT COMPLEX. 



The Basement Complex rocks in the area studied comprise gneissoid 

 granites, biotite-schists, and hornblende-schists, cut by dikes of greenstone 

 and by veins of quartz and granite. The granites are best exposed in the 

 NE. 1 sec. 7 and the NW. ^ sec. 8 and the NE. i sec. 7, T. 42 N., R. 28 W., 

 where they occur as bare knolls of a fairly coarse pink rock, separated 

 from one another by stretches of sand. The best exhibition of rocks with 

 the typical aspect of the Basement Complex is along the west half of the 

 east-west quarter line of sec. 19, T. 42 N., R. 28 W., and south of the center 

 of this section. Here we find hornblende-schists and hornblende-gneisses 

 cut by veins and dikes of red granite and by greenstones that are usually 

 schistose. Near the west quarter post of the section is a high hill bare of 

 vegetation. On this hill the rocks are especially well exposed. In addi- 

 tion to the types already mentioned, there is present here a coarse white 

 pegmatitic-looking granite that apparently cuts the hornblende-gneiss. 



All the members of the Basement Complex in this area are so similar 

 to the corresponding members of this complex elsewhere in the Lake Supe- 

 rior region that they demand but little description. They are described 

 here only in sufficient detail to establish their character. 



THE GNEISSOID GRANITES. 



The gneissoid granites north of the fragmental tongue,, and those of 

 the two areas surrounded by the sedimentary rocks, are mediumly coarse 

 aggregates of a dark-red feldspar, white quai'tz, and a dirty green chloritic 

 substance. The red feldspar is in excess, sometimes to the exclusion of the 

 other components, when the hand specimen resembles a dense red felsite. 

 Almost all specimens are gneissoid. The constituents are usually lenticu- 

 lar, but in a few specimens, particularly those taken from near the contacts 

 with the sedimentary rocks, they are di-awn out into long slender string-like 

 masses, giving the specimens a streaked appearance. 



The microscopical features of all the granites are those common to these 

 rocks elsewhere in the Basement Complex. They consist of clouded ortho- 



