Page:The Journal of geology (IA journalofgeology11893univ).pdf/289

ders appears to be identically the same granite as that on which the conglomerate rests. We find both the white and the red-weathering varieties represented among the pebbles of the conglomerate, and perhaps also the coarse pegmatite. Figures I and II from a sketch made to scale in the field show the appearance of the rock on the dip surface, while Fig. III, drawn to the same scale, shows the outlines of two medium-sized granite bowlders, as seen in cross section on a joint plane.

At the south end of the main exposure, a nearly vertical cross joint plane on the south of which the rocks have been removed, shows the contact for eight or ten feet across the strike. The relations are represented in Fig. IV.

The conglomerate can be followed by its pebbles with great certainty. The granite below is equally unmistakable. Between the lowest pebble layer of the conglomerate and the undoubted granite, is a zone a few inches wide, that is difficult to assign with certainty to either rock. The contact otherwise is very definite and follows the dip of the conglomerate pebbles. There is no indication that the contact is not simply one of erosion. As the matrix of the conglomerate has been transformed into a crystalline schist as the result of shearing, one may easily suppose that the doubtful zone represents either recomposed granitic detritus or the broken up material of both rocks due to movement along the contact during the folding.

At the north end of the main exposure we have another natural section on a cross vertical plane, shown in Fig. VI. Here a large semi-detached mass of granite, which seems to be joined at the east end to the main mass, lies over a portion of the conglomerate. At its west end it includes a folded fragment of the conglomerate matrix four or five feet long, and two or three feet across, shown at B in the figure.

The junction between the quartz-schist and the granite is sharp, and the banding of the schist is cut at a small angle by the granite. At the east end of the granite mass, at A, a ver-