Glacial Erosion in Norway. 229 
these conditions belong only to valleys of great mountain ranges. 
However, there is one condition under which glaciers, when shod 
with graving tools, ought to be great eroders, viz., when their 
motion is much more rapid than the flow of land ice,—which is 
almost invariably less than three feet a day, under which condition, 
included stones commonly adhere by friction to the subjacent rocks, 
and cause the lower surfaces of the ice to be grooved. This condi- 
tion of extraordinarily rapid: movement has been seen at Jacobs- 
havn glacier in Greenland, where Professor Helland! found a velo- 
city of from forty to sixty feet a day. In Alaska, Lieutenant 
Schwatka? and Professor G. F. Wright? observed glacier move- 
ments of from forty to seventy feet a day. In these cases the gla- 
ciers are moving into the sea, and the new element of partial flota- 
tion or sliding, which does not belong to land glaciers, is here intro- 
duced. The great velocity of these glaciers is far beyond any 
observed ability of ice to flow as plastic bodies; consequently, one 
is led to conclude that, under partial flotation, stones may be held 
firmly as graving tools by glaciers. 
Hereby we are able to explain. the occurrence, in many Alpine 
valleys, of a greater glaciation than we see in progress to-day, as 
being due to glaciers rapidly advancing into fjords, during a period 
of partial submergence. 
The appeal to the greater magnitude of the glaciers, as produc- 
ing effects not now seen as the result of those of the present day, 
Seems to be begging the question, for the action of thicker glaciers 
differs from that of thinner in amount rather than in kind; for 
increased pressure, raising the temperature, increases the plasticity 
of the ice, as it is seldom if ever lower than freezing point. Con- 
Sequently it seems improbable that stones should be held more 
firmly in glaciers of thousands of feet in thickness than in those of | 
hundreds of feet. In addition, the friction between the stones held 
m the ice, and the surface of the subjacent rock, is proportionally 
increased by the greater weight of the glacier. 
Over the vast area of action, the work of floating or sea-ice, in 
some forms, is enormous. On the northern side of Hudson Strait, 
i a ords of North Greenland, Quart. Jour. Geo. Soc., 1877, A. Hel- 
n 
z “Times” Alaska Expedition, New York, 1886, Schwatka. 
The Muir Glacier, Am. Jour, of Sci., 1887. l 
