1877 *] The Loess of the Rhine and the Danube. 85 
ice, the effedt must have been that that southern slope would 
advance southward ; so that the ice would progress not only 
by flowing southward as a glacier, but by the area of frozen 
precipitation being moved southward. Let us suppose that 
a ridge of ice 6000 feet high, on Greenland, would intercept 
all the moisture of the southern winds ; then, if the precipi- 
tation every year on its southern slope was greater than 
what it lost by melting and evaporation, it must have ad- 
vanced southward, and no depth of the ocean bed would 
prevent it doing so, so long as the excess of frozen precipi- 
tation continued. 
Some geologists urge as an objection to the theory of the 
great advance of circumpolar ice, that it cannot be pushed 
up a slope by a force adting from a distance. In the words 
of the most eminent of these, the Duke of Argyll, “ the 
theory assumes that masses of ice lying upon the surface of 
the earth more than mountain deep would have a proper 
motion of its own, capable of overcoming the fridtion not 
only of rough level surfaces, but even of the steepest gra- 
dients, for which motion no adequate cause has been 
assigned, and which has never been proved to be consistent 
with the physical properties of the materials on which it is 
supposed to have adted.”* If this was a fair statement of 
the views of glacialists a very strong case would be made 
out against them, for it is evident to any one having a mo- 
derate knowledge of mechanics and of the physical properties 
of ice that it could not be moved in such a manner ; and 
Prof. James Forbes proved many years ago that, even when 
flowing down the steep slopes of the Alps, the bottom layers 
of the ice are so retarded by the fridtion of the rocks beneath 
them that the upper ones slip over them, producing the 
strudture he named “ frontal dip.” But it is not a fair 
statement of their views. Mr. Thos. Jamieson, one of the 
greatest authorities on the glaciation of Scotland by land 
ice, showed, in 1865, that if snow was heaped up it would 
spread out at the base, and flow off <£ not so much on ac- 
count of the inclination of the bed on which it rested as 
owing to the internal pressure exerted by the immense accu- 
mulation of snow,”t and he further compared its movement 
to that of a heap of grain which flows off when poured down 
on the floor of a granary, the grains flowing over each other 
and spreading out with a very small pitch or slope. Prof. 
Dana, too, has entered very fully into the question of the 
* Nature, vol. xiv., p. 436. Report of Address to Brit. Assoc, at Glasgow. 
f Quart. Journ. Geol. Soc., vol. xxi., p. 166. 
