The Madison Type of Drumlins. — Upham. 79 
drift which had become superglacial, being exposed on the 
ice surface by ablation. Loaded with these materials, the 
superglacial streams encountered crevasses, down which they 
plunged. AVholly beneath the ice-sheet, or within its lower 
part, at the level whence the waters flowed away under or 
within the ice, bearing their finer silt and clay onward, the 
beds forming the center of these hills were accumulated. In 
the case of the Madison drumlins, the avenue of outflow of 
the subglacial or more probably englacial stream appears to 
have been the col, now a swamp about 85 feet above lake 
Mendota, which divides that lake basin from the Black Earth 
river flowing into the Wisconsin river (figure 1, plate in). 
The locations of the three large drumlins in Madison which 
are known to enclose stratified sand and gravel as their cen- 
tral and chief masses, forming an east to west series, seem to 
me to point very surely to their close relationship in origin. 
When this Green Bay lobe of the ice-sheet receded from its 
Kettle moraine, convergent slopes of its surface from the north 
and south and from a considerable area eastward probably 
turned the waters of its melting and of rains toward the east 
to west line of these hills and toward the Black Earth col. 
The principal stream of this depression upon the ice, falling 
through crevasses during several or many summers, appears to 
have amassed first the chief part of the Observatory hill, and 
afterward successively the nucleal beds of the University and 
Capitol hills (figures 2 and 3, plate in). 
Not only these great accumulations of sand and gravel were 
so deposited, but also similar beds were laid down on the low- 
lands and overspread by till west of the Observatory hill and 
east of the University hill. A series of eleven borings by 
Prof. F. H. King on the Agricultural Experiment Station 
farm, along a line one-fourth of a mile long from south to 
north passing across the western base of Observatory hill, 
found the till to range from 8 to :><) feet in thickness, attain- 
ing its maximum at the end of the longer axis of the hill, 
where a boring was stopped at 20 feel by a boulder. All tile 
other borings of the series passed through the till and went 
several feet in gravel, which undoubtedly i^ continuous with 
the chief mass of the hill. On the Mat and slightly lower sur- 
face within a sixth of a mile farther west the superficial (!<•- 
