482 PROCEEDINGS OF THE ACADEMY OF [1892. 



is a terrace scarcely 100 feet high. I very much question whether 

 there are any "glaciated" pebbles in it. Certainly the whole 

 country around through which we drove for a considerable distance, 

 does not show signs of glacial action. I should say that the occur- 

 rence of scratched stones in that vicinity conclusively proves that 

 such striation can be produced by other causes than glacial ice. 

 The same is, perhaps, true of Professor Salisbury's other isolated 

 cases at Bethlehem and Sunbury, and probably support my 

 inferences concerning the deposits at High Bridge and Pattenburg. 



The conglomerate boulders between Monmouth Junction and 

 Deans are not over 100 feet above sea-level, and there is no higher 

 land between them and the Delaware at Trenton. They may, 

 therefore, easily have been floated into their present position during 

 the flooded condition of the lower Delaware Valley, when the depos- 

 its of Philadelphia red gravel and brick clay (the Columbia) took 

 place. 



The facts already presented concerning the extension of glacial 

 ice on the east side of the Delaware River for several miles south of 

 Easton, furnish the key to the perplexing phenomena of the Lehigh 

 Valley below Bethlehem. The fringe of glacial ice deposits extends 

 southward to the vicinity of Easton, and westward to the divide 

 between Bushkill and Monocacy creeks in the vicinity of Nazareth. 

 The evidence is not yet as complete as I would like, but there is 

 already enough to give a great degree of certainty. 



It is significant that Monocacy Creek north of Bethlehem is per- 

 fectly free from pebbles — the natural reason being that it has its 

 course over limestone and slate formations which furnished none. 

 If these formations had been overrun by glacial ice, this would 

 not have been the case. On the other hand, Bushkill Creek has 

 them in abundance. The only difference between the creeks is that 

 boulders had been scattered over the headwaters of the Bushkill by 

 the ice, and not over those of Monocacy. That the ice extended 

 nearly, at least, to the watershed between the creeks seems certain, 

 from the fact that large boulders of Medina occur in considerable 

 abundance on the slate hills two miles north of Nazareth, at a height 

 of about 400 feet above the Bushkill. 



The Lehigh, from the Gap to Easton, flows through or across the 

 Hudson River Slates and Trenton Limestone, which so persistently 

 border the Blue Ridge all along the Atlantic coast. For some 

 reason, the surface of the limestone belt is pretty generally from 200 



