DISCUSSION OF GLACIAL PHENOMENA. 17 



sidual clay and alkiviuin and weathering rock-cliffs, such as are found in the Wis- 

 consin driftless area and south of the glacial boundary. The smooth contour of 

 this outer drift, as compared with the hilly and knolly moraine and mostly quite 

 uneven drift-sm^face from thence northward, seems due to less energetic glacial 

 action when the ice-sheet was being accumulated, and reached farther than during 

 its recession, when its rapid marginal melting probably gave a much steeper frontal 

 slope, with stronger glacial currents. Any slight halt or re-advance of the ice, 

 produced by a series of somewhat colder years and heavier snowfall than usual, 

 would then be marked by a moraine. Since the moraines seldom are well devel- 

 oped on the extreme boundary of the drift, it seems better to call them marginal 

 or retreatal moraines, rather than terminal, although at the time of its formation 

 each was at the receding termination of the ice-sheet. 



Frank Leverett : 



The explanation and diagram given by Mr Upham to show his conception of 

 the origin of the ' ' fringe " on Long island does not seem a satisfactory explanation 

 for the more western field between the, Alleghany mountains and the Missouri 

 river. The drift outside the moraine in that region bears evidence in the degree 

 of surface oxidation and erosion of a great lapse of time between its deposition and 

 the formation of the moraine which seems to be the correlative of the Long Island 

 moraine. 



W J McGee : 



The excellent communication by Professor A. A. Wright is an especially gratify- 

 ing presentation of facts and inferences relating to the region described. As is 

 well known to the Society, the phenomena of the region has given rise to certain 

 differences of opinion, and diverse opinions have been expressed at earlier meet- 

 ings, nota))ly the last summer meeting at Rochester. 



Even before the institution of this Society certain superficial deposits of northern 

 New Jersey, specifically those flanking Delaware river, were correlated with the 

 early Pleistocene Columbia formation, and from the sum of the phenomena of this 

 formation the existence of ancient glacial deposits in or not far north of the region 

 was inferred, though the ice-laid deposits were not actually observed. Subse- 

 quently a detailed official survey of the region was undertaken by Professor E. D. 

 Salisbury, under the joint auspices of the United States Geological Survey and the 

 State Survey of New Jersey, and at the summer meeting of the Society in Wash- 

 ington (in 1891) Professor Salisbury announced the discovery of old glacial deposits 

 many miles outside of the terminal moraine at different points in northern New 

 Jersey. Later studies by the same geologist, in some of which I had the pleasure 

 of participating, resulted in the discovery of other remnants which were inferred 

 to represent a once continuous drift-sheet long antedating the moraine-fringed 

 drift and grading into the Columbia formation. At the Rochester meeting, how- 

 ever, a different interpretation was jjlaced on the phenomena, which were in part 

 ascribed to local causes such as soil-cap movement, and in part described as that 

 shadowy omnibus for the unknown, called the " fringe," and this despite the con- 

 tention of skilled geologists familiar with tlie phenomena. Accordingly the sub- 

 stantial adoption of Professor Salisbury's main contention is especially gratifying. 

 It is none the less gratifying that Professor Wright goes even further in his inter- 

 Ill— Rum,. GKor,. Soo. Am., Vol. 5,1893. 



