734 ABSTRACTS OF PAPERS 



the basal ice did not clog. Such basal movement was probably due to the ice 

 being shoved bodily forward by the vigorously advancing ice in the rear, this 

 forward shove being superimposed on such internal flowage as was taking 

 place. It is believed that the application of such propulsive force in the re- 

 gion of the center of radiation of such a mass, which was tending to lag in 

 every part, owing to great friction, would tend to cause the longitudinal lines 

 of flowage to spread and so develop stress along transverse lines. These 

 stresses, though perhaps not causing the actual opening of longitudinal cre- 

 vasses, would facilitate spreading of the ice about obstructing piles of drift 

 and their being shaped into drumlins rather than their obliteration by erosion. 

 It might also induce localized deposition in piles or ridges which would later 

 be shaped and might be added to by the plastering on of drift. Computations 

 based on the ice streams forming the second set of drumlins show the radia- 

 tion to have been even more marked than in the first case with correspondingly 

 greater crowding forward of the faster moving ice in the rear and more 

 marked development of drumlins. Comparison with segments of the glacier 

 which had equal initial widths, but did not form drumlins, shows that in the 

 latter there was very moderate radiation and that, unless the ice in the rear 

 was moving more slowly than that in front, there was a decrease in the vol- 

 ume of the stream as it advanced, as opposed to the increase in volume of the 

 drumlin-forming stream. With the radiation fully accounted for by the 

 spreading of the ice under its own weight and with no forward crowding of 

 the ice in mass there would be absence of lateral stress and of the tendency 

 to longitudinal crevassing, and this may explain the absence of drumlins. 

 Other factors than radiation are probably also involved. 



Discussion 



Prof. H. L. Fairchild : For Dr. Alden's paper and its illustrations and man- 

 ner of presentation, I have great admiration. It is interesting to note the 

 similarity in all important features between the Wisconsin and the New York 

 drumlins. The production of these singular masses of drift evidently depends 

 on the combination of several factors which do not commonly occur over the 

 glaciated field, one important and essential factor being the movement of the 

 ground contact ice due to thrust or push of the rearward ice. The amount 

 of basal drift necessary to construct drumlins is probably prohibitive of free 

 or gravitational flow of the burdened ice on gentle slopes. As drumlins in 

 New York lie on slopes facing or opposing the ice advance, the movement 

 necessary to vigorously mold the ground moraine could not be produced merely 

 by the gravity of the drumlin-shaping ice. The only point in Dr. Alden's fine 

 discussion that I would question is the causal relation of the spreading or 

 radial flow of the ice to the drumlin-building process. In several localities in 

 New York we have groups of drumlins where the ice did not have spreading 

 movement. I should say that the radial movement of the ice was an accom- 

 paniment of the more favorable drumlin-forming conditions, but not an essen- 

 tial factor, 



