292 The A>7ierican Geologist. November, \>m 
washed away from superglacial drift, exposed by ablation, 
mostly within ten to twenty miles back from the edge of the 
ice, and at altitudes ranging from 50 or 100 feet to 1,000 feet 
above the land. To such altitudes we may believe that drift 
was borne upward into the basal part of an ice-sheet a mile 
thick, if we may draw a proportional estimate from the Malas- 
pina glacier of Alaska, and from the observations by 
Chamberlin, Drygalski, and others, concerning the plenti- 
ful englacial drift in the lower part of the terminal cliffs of the 
Greenland icefields. Moreover, in the esker of Bird's Hill, 
near Winnipeg, Manitoba, I have found conclusive proofs that 
nuich englacial drift, becoming at last superglacial, existed 
there at bights exceeding 500 feet. 
Another evidence of glacial rivers is supplied by water- 
worn pot-holes, called in German and in the Scandinavian lan- 
guages "giants' kettles," which were bored in the bedrock be- 
neath glaciers or an ice-sheet by torrents of water falling 
through deep moulins. This name, moulin, coming from the 
French and meaning a mill, is applied to a vertical tunnel, 
melted at first by the waters of the surf?ce trickling into some 
very narrow crevasse that has just begun to open, until, after 
enlargement by this dissolving action, it receives sometimes 
a large stream, such as could not be waded, pouring with r 
thunderous roar down a cylindric shaft to the rock floor under 
the ice. The esker rivers belonged to the closing stage of the 
Glacial period; but the torrents eroding glacial pot-holes in 
Scandinavia, Switzerland, and the United States, appear, as 
will presently be explained, to have attended the accumulation 
of the ice-sheets. The streams that bored these pot-holes or 
giants' Icettles were very small, and were only very scantily 
drift-laden, in comparison with the rivers which formed the 
great esker ridges. 
In the close vicinity of Christiania, Norway, numerous 
giants' kettles have been discovered and cleared of the glacial 
drift and water-rounded stones which filled them. The locality 
of greatest interest is Kongshavn, a southeastern suburb on 
the shore of the Christiania fjord, where, between the lines of 
low and high tide, a glacial pot-hole eroded in gneiss was 
found, on the removal of its drift contents, to be t6 feet deep, 
with a diameter of 5 feet. Another pot-hole, from which the 
