202 PROCEEDINGS OF THE ACADEMY OF [1895. 



Lesley calls attention to the curious fact that the gravel deposit at 

 Easton stands nearly upon the same level with the highest of the 

 Upper Delaware terraces above that river. 



The terraces of the Upper Delaware are a marked and beautiful 

 feature of its scenery. They are found between Port Jervis and the 

 Water Gap, often as four regular steps. The first or lowest is from 

 20 to 25 feet above the river, while the fourth or highest terrace 

 stands at 150 feet above the present river level. Five terraces are 

 all well marked along Brodhead's Creek, the principal tributary of 

 the Delaware between Port Jervis and the Water Gap. They can 

 also be traced up the "great buried valley" in which the sluggish 

 stream known as Cherry Creek flows to enter the Delaware just be- 

 low the mouth of Brodhead's Creek and just above the northern 

 entrance to the Gap. 



In Report L, Prof. Lewis says, " these terraces of the Upper 

 Delaware may be due to an ancient obstruction in the Gap backing 

 up the water from the melting glacier to form a lake of considerable 

 size." That these terraces are of later formation than the glacial 

 deposits is proved on Brodhead's Creek, where a railroad cutting shows 

 kames partly covered by terrace material. 



Now it will be remembered their positions are directly reversed at 

 Easton ; there the glacial material lies on the top of the river terrace, 

 showing that the terrace there is the older deposit of the two. 



If the rock in the centre of the amphitheatre of the pre-glacial 

 gorge had not been cut down to present river level, when the glacier 

 retreated this rock-wall would certainly stand as "an ancient obstruc- 

 tion in the Gap, damming back the waters to form a lake of con- 

 siderable size," or from Port Jervis to the Water Gap. In this lake 

 the waters would rise until they reached the top of the rock-wall and 

 pouring over it the draining of the lake would begin. So the highest 

 terrace of the new river would come to stand nearly upon the same 

 level as the lowest or last of the old river, the new standing at 150 

 feet and the old at 170 feet above the present water level in the 

 river. Does this difference of 20 feet represent the sum of the 

 fall of the bed of the old river between Easton and the Water Gap 

 and the amount of the erosion by the ice between the same points? 



In Vol. L, page 58, H. Carvil Lewis says, "it was a surprising and 

 unexpected fact to find no tongue of ice was projected through the 

 Gap, which was, as it were, ignored by the glacier. It filled the 



