Page:The Journal of geology (IA journalofgeology11893univ).pdf/276

derived from a stream of drift passing over the quartzite ledges and making constant additions from them.

2. The drumlins are found to be filled with quartzite erratics immediately in the lee of the ledges. There are even drumlins which lie directly upon the ledges and envelop them in large part, which are found free from local quartzite derivatives on their stoss ends, but are inset with them in their lee ends. The quartzite content of the leeward portion ranges, in observed sections, from 5 per cent. to 10 per cent. of the whole drift. In one case, Mr. Buell found an isolated drumlin to contain all of the quartzite of its particular kind observed in the vicinity. It evidently completely envelops the parent ledge and retains the most of its derivatives. Several bowldery mounds, that may be regarded as drumlins in miniature, occur in the immediate lee of the ledges, in which the quartzite drift was estimated to comprise from 20 per cent. to 75 per cent. of the whole. The material, in these instances, appeared to be chiefly former talus of the quartzite outcrops. Setting in thus promptly immediately at the quartzite outcrops, the erratics are found to diminish very markedly in proportion as the distance increases. A mile and a half away from the outcrops, a careful estimate of the quartzite content gave 3 per cent. of the whole mass of the drift. The average for the area between 1 and 6 miles is 1-1½ per cent.; between that and 20 miles 1 per cent.; between that and 45 miles .364 per cent., and in the terminal moraine .0477 per cent. The surface distribution shows a similar diminution. The estimated amount of quartzite on the very bowldery mounds near the ledges was 17,700 cords; at other points within six miles of the outcrops 12,650 cords; at medial points 1,409 cords; on the terminal moraine, about 45 miles distant, 747 cords. This very rapid diminution in the quantity of quartzite erratics is significant in showing that the element of resistance to transportation was an influential factor. This is precisely what is to be anticipated on the hypothesis that these bowlders were pushed or dragged along the base of the ice. It seems very far from what is to be expected, however, on the