1892.] NATURAL SCIENCES OF PHILADELPHIA. 483 



to 300 feet lower than the slate. Indeed the limestone is rarely 

 more than 200 feet above the river. Hence it is within reach of 

 the regular Columbia deposits. It is therefore difficult to tell 

 whether the distribution of glaciated material over this area about 

 Bethlehem and toward Easton was by direct glacial action or by the 

 aid of water. The extension of the ice past the mouth of the 

 Lehigh would indicate a good deal of disturbance in the drainage 

 of the river, and I am inclined to recognize that agency in account- 

 ing for many of the facts. The terraces at Bethlehem are not over 

 200 feet above the river. If, however, it be true that Professor 

 Salisbury has found glaciated pebbles 500 feet above the river on 

 the mountain south of the city I should grant the extension of the 

 glacier to that point. But such an extension seems to me improb- 

 able, from the lay of the land. The glacier which surmounted 

 Blue Ridge at Offset Mountain, and in its retreat piled up the vast 

 moraine at Ackermansville, may well have fanned out to cover the 

 hills north of Nazareth, and it certainly deposited a moraine of 

 considerable dimensions near Shimerville, about five miles north of 

 Easton. But it seems unlikely that it could extend as far as Beth- 

 lehem, and since we have other causes in the field to easily account 

 for all the facts that appear there, we need not make the supposi- 

 tion. Floating ice in a river valley gorged as this was both by bergs 

 from the glacier further up, and by land ice at its mouth, is cause 

 sufficient, and there is no need of asking for more. 



The conclusion of the whole matter is : — 1st, That on the Atlantic 

 coast, as in the Mississippi Valley, there is usually a fringe of thinner 

 glacial deposits extending a few miles more or less, south 

 of any well defined moraine. 2d, That this fringe is lim- 

 ited in the east branch of the Susquehanna by Montour's 

 Ridge at Bloomsburg. That all the higher glacial deposits 

 below that point belong to the Columbian era, and do not 

 extend anywhere much above 200 feet above the river, while 

 at Harrisburg they are limited to about 180 feet. 3d, That in the 

 Delaware Valley the ice extended about six miles past the mouth of 

 the Lehigh, and for several miles northeastward was limited by 

 Musconetcong Mountain, and then drew back to the rear of 

 Pohatcong Mountain. Farther east, however, these mountains both 

 come again into the range of the ice movement. 4th, That the 

 lower part of the Lehigh was specially clogged with ice, so as to 

 increase the floods for some distance up toward the Gap, but the ice 



