366 G. F. Wright— Unity of the Glacial Epoch. 



in this portion of the state there has been absolutely no trans- 

 portation of northern material out upon the Triassic shales, 

 showing- that no glacial movement here ever passed Muscon- 

 etcong Mountain. 



These Archaean ridges everywhere exhibit remarkable effects 

 of secular disintegration. Gneissoid bowlders are creeping 

 down their sides in all directions of slope, and, in favorable 

 places for observation, the rock is seen to be disintegrated to a 

 great depth. Many cuts show that the softer material is wash- 

 ing out and working down toward the valley, and leaving 

 the harder masses to follow at a slower rate. Doubtless 

 the original height of the mountain has been thus reduced 

 thousands of feet, thus entirely removing the covering of 

 lime and slatestone. We have here now but the cores of 

 the original ranges. But guided by the material trans- 

 ported by what we may call the Delaware River lobe of the 

 ice sheet, we find that in the vicinity of the river the ice 

 actually overran Scott's Mountain as far east certainly as 

 Bethel, and left Medina bowlders in considerable numbers in 

 the Pohatcong Valley near Washington. The actually trans- 

 ported material here cannot be distinguished in its oxidation 

 from that in the moraine north of Oxford Furnace. The oxi- 

 dation of which Professor Salisbury speaks at Oxford Furnace 

 and Little York is the secular oxidation which we have 

 described as characterizing the whole mountain. But with 

 this local material at the places mentioned there is mingled on 

 the surface a considerable deposit of the northern rocks 

 belonging to the fringe. The ice here barely went over 

 Scott's Mountain to Washington. It did not here cross Po- 

 hatcong Mountain so as to reach Musconetcong Mountain. 



Nearer, the river, however, it crossed the low Pohatcong 

 ridge also and, at one point, about five miles south of Philips- 

 burgh, reached a col in Musconetcong Mountain, landing 

 there a good many Medina bowlders, and allowing some of 

 them to be carried down a small streamlet on the south side 

 which for a time offered an outlet for the drainage in that 

 direction. That the ice did not extend farther is shown by 

 the fact that there is absolutely no transported material out on 

 the Triassic rocks beyond the influence of this little stream, 

 and in the case of that, the Medina pebbles have all worked 

 down towards the Delaware River. 



On the west side of the Delaware, below the moraine, 

 there is a similar extension of the phenomena of the fringe ; 

 as there is also in the Valley of the Susquehanna below Ber- 

 wick. To obtain the sections of these river valleys given by 

 Mr. McGee to prove a subsidence in that region of several 

 hundred feet during the Columbia (Philadelphia Brick Clay) 



