South of the Terminal Moraine. 277 
serious attempt has been made to construct a satisfactory hypoth- 
esis of its origin. . . . A long, straight, sharp-crested ridge, 1000 
eet high on a base two miles wide, is here, not split by a fault, 
nor gapped by a stream, but worn smoothly through to half its 
altitude. The raggedness of the mountain crest ceases and 
smoothly rounded slopes descend to the smoothly rounded bottom 
of the gap which is lined with sand and gravel. . . It is evidently 
a deep cross-groove smoothly made and finished by some agent of 
- erosion acting slowly and continuously—but an agent quite differ- 
ent from a river... . I can see no serious objection to the sup- 
position that the front of the ice-sheet may at one time have ad- 
mountain at the Wind Gap. . . . In any 
€ origin of the Wind Gap the fact that there extends south- 
ward from the level of the bottom of the Gap, a fan-shaped slop- 
ing plain of rounded bowlder drift which has evidently all come 
through the Wind Gap, and has probably been brought through 
it by the agent which made the gap (although that cannot be 
taken for granted) must be taken into consideration.” 
Professor Lesley then repeats an explanation for the origin 
of the Wind Gap which he made in 1882, that it was due to 
the overflow of a vast lake which he supposed to cover a large 
part of Monroe and Carbon Counties, which lake was due to a 
great ice-dam at the Lehigh Water Gap. But as this dam 
Would have had to be 1100 feet high in order to deliver the 
water over the crest of the mountain when the Wind Gap was 
gun, and as the glacier did not cover the region about the 
Lehigh Gap, he grants that such a supposition is untenable. 
-) He then mentions a topographical feature six miles west 
of the Lehigh Gap, saying : 
“Tt looks as if the bowl had been made by some kind of water- 
fall; but if so the mass of water must have been extraordinarily 
_ great and must have shot clear of the top of the mountain—an 
_ alrangement only possible in case the back valley were filled with 
ice to a height exceeding that of the mountain.” 
In addition to the passages just quoted, there are a number 
of other statements made by different geologists which describe 
further supposed evidences of glaciation in Pennsylvania south 
of the terminal moraine. 
(5.) Mr. ©. E, Hall has published two short papers which are 
ag Sains in the preface to Report Z. In the first of these* 
he calls attention to the bending over of slate outcrops both 
horth and south of the Lehigh Gap, which he regards as due to 
the southeastward movement of a glacier. 
(6.) Mr. Hall also mentions a mass of debris a few hundred 
6 
yards north of the gap, concerning which he says: 
3 Proc. Amer. Philos. Soc., xiv, 620. 
