C. H. HITCHCOCK THE CONNECTICUT VALLEY GLACIER. 



A free discussion followed the reading of this paper. Professor W. H. 

 Mies, speaking of his observations in the Alps, said — 



About the Matterkorn and the Weisshorn I have observed thin glaciers with a 

 movement different in direction from the thicker glaciers which formerly existed 

 in the same places. I believe that under some conditions the upper surface of a 

 wlacier mieht have a different direction of movement from the lower surface, and 

 have seen glaciers moving over till, kanies. etc. In one instance I had the fortune 

 to observe under favorable conditions a -lacier passing over a surface sparsely 

 strewn with bowlders, and at one point found that a bowlder was being slowly 

 pushed forward by the ice, but at the same time the body of the glacier moved 

 much more rapidly than the bowlder, so that its bottom was marked by a long- 

 groove extending some yards down stream from the bowlder. 



Professor I. C. White observed — 



Contrary to my former belief, I now know of no mountains in northern Penn- 

 sylvania which were not buried in the Pleistocene ice sheet. 



Mr McGee remarked — 



The paper and the discussion suggest a feature ofice movement not alwaysappre- 



ciated. which is well exemplified in northeastern Iowa about the margin of the 

 driftless area. There were in this region two ice invasions of approximately hut 

 not exactly equal extent : in the first the ice advanced farther in the north and 

 not so far in the south as in the later invasion, so that the drift borderingthe 

 driftless area represents the lower till or older sheet in the north, the upper till or 

 later sheet in the south. >s~ow both in the north, about the headwaters of < >neota 

 river, and in the south, about the lower reaches and tributaries of the Maquoketa, 

 there is a remarkable relation between the elements of the topography and also 

 between the distribution of the drift and the surface configuration — a relation best 

 displayed in southeastern Jackson county and northeastern Clinton county. Here 

 the characteristic curves of the glacial topography pass gradually into the more 

 strongly accented lines of the water-cut topography by which the driftless area is 

 distinguished, and it is significant that the transition from ice-molding to water- 

 carving is not only horizontrl hut vertical — that first the bottoms, later the mid- 

 sides, and finally the rims of the valleys lose the glaciated curves and assume the 

 water-cut angles ; and this is especially true of the transverse valleys. Moreover 

 in some cases the transverse valleys are partly lined with an ice laid deposit differ- 

 ing from the prevailing drift of the region in that it is made up almost wholly of 

 local debris, sometimes apparently removed lint a few feet or rods from the parent 

 ledges; while even the furthermost traces of the drift are made up predominantly 

 of far-traveled crystalline rocks, and occupy faintly glaciated summits some miles 

 beyond the limit of ice-molding in the valleys. In brief, Loth the distribution of 

 the drift and the topographic configuration indicate that the thin margin of the ice 

 bordering the driftless area first pushed into and filled certain transverse valleys. 

 and then rode over the imprisoned ice as on a bridge, the surface of slip being 

 transferred from the bottom of the valley to the plane of its rim. In valleys oblique 



