Page:The Journal of geology (IA journalofgeology11893univ).pdf/284

The lowest member of the Lower Huronian rarely outcrops in the Republic trough. Brooks on his large scale map of Republic Mountain and vicinity, in 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^[1] 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.

The accompanying map will make plain the immediate relations between granite, quartzite, and magnetite-actinolite-schist. The magnetite-actinolite-schists occupy a broad belt in the northern 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.