478 PROCEEDINGS OF THE ACADEMY OF [1892. 



other places. They were also noticed on the slate rocks at Bangor. 

 I have taken pains this summer to revisit some of these places, and 

 am more than ever impressed with the fact that a small scratched 

 surface, and a limited number of scratched pebbles do not prove a 

 glacial period. Near Ackermansville, in Northampton County, Pa., 

 I observed excellent strise on the slate rock in a railroad cut, made by 

 the loose material which has slid down the bank since the cut was 

 opened a year or two ago. I also succeeded in securing well marked 

 scratches on slate pebbles by an artificial slide which I myself pro- 

 duced in the bank at Pattenburg. 



It is fair to say, however, that we found evidence of the true 

 fringe of the ice age so near to both High Bridge and Pattenburg, 

 that it is not much of a strain on the scientific imagination to 

 suppose that the ice here just crossed over Musconetcong Mountain 

 and ended for a while at these points. But that this was not the 

 case, I think is evident from the considerations following: — 



1st. The cause already adduced is entirely competent to produce 

 the results. There is no occasion to introduce a greater cause. 



2d. The absence, as just stated, of all material foreign to the im- 

 mediate locality, demonstrates the local character of the cause. 



3d. The appearance of foreign material as an overwash gravel in 

 the valley of the Musconetcong River, eight or ten miles to the 

 northwest just beyond Junction, shows that foreign material would 

 have been brought by glacial ice, had it extended so far. Here 

 pebbles of the enduring and well defined Medina sandstone, and 

 Oneida conglomerate, appear to a considerable extent, derived 

 probably from the moraine to the northeast, in which it has its 

 headwaters. But on the low summits of the parallel Pohatcong 

 Mountain, south of Washington, we failed to find any foreign mate- 

 rial in two cross sections which we made under favorable circum- 

 stances. In the valley of the Pohatcong, at and below Washington, 

 however, the foreign material is so abundant and of such size as to 

 make it probable that the glacial ice overrode Scott's Mountain. 

 Boulders of the Medina and Oneida sandstones occur here south of 

 Pohatcong River, in connection with a deposit of large extent of 

 finer material capped with loam and clay. The railroad also makes 

 two other good sections in till south of the mountains. From this 

 point on to the north these characteristic foreign boulders are i 

 found at frequent intervals on the road leading up the south side of 

 Scott's Mountain toward Oxford Furnace, to a height of 360 feet 



