A CONTACT BETWEEN THE LOWER HURONIAN 



AND THE UNDERLYING GRANITE IN THE 



REPUBLIC TROUGH, NEAR REPUBLIC, 



MICHIGAN. 



I. 



The lowest member of the Lower Huronian rarely outcrops 

 in the Republic trough. Brooks on his large scale map of 

 Republic Mountain and vicinity, 1869, shows but two exposures 

 of the lower quartzite. They lie south of the mine, in the bend 

 of the horseshoe, and were discovered by Pumpelly and Credner 

 in 1867. Some 250 or 300 feet southwest of the westernmost of 

 these, I have recently found a conglomerate resting upon granite, 

 the contact of the two rocks being very well exposed. It is 

 interesting to note that the locality is very close to that figured 

 by Brooks^ to show that the strike of the quartzite and of the 

 magnetite-actinolite-schist just above it, runs directly across the 

 foliation in the underlying gneissoid granite. From this he 

 inferred an unconformability between the Huronian and the 

 Laurentian. 



II. General Relations. 



The accompanying map will make plain the immediate rela- 

 tions between granite, quartzite, and magnetite-actinolite-schist. 

 The magnetite-actinolite-schists occupy a broad belt in the north- 

 ern part of the area represented on the large scale map (Fig. V), 

 striking between N, and E. at various angles, and dipping W. of 

 N. from 35°-40°. The alternating layers of silica, actinolite, 

 and magnetic, or two or all combined, which compose this rock, 

 show both a considerable degree of plication, and also a coarse, 

 cross cleavage which strikes between N.45°W. and N. 60° W., 

 or roughly in the direction of the axis of the trough. 

 ^Geology of Michigan, Vol. I, part I, p. 126. 



