chap, vnr.] THE CAUSES OF GLACIAL EPOCHS. 
135 
with North-eastern Canada seems to have been the source of 
much of the glaciation of that continent. 1 
The reason why no accumulation of snow or ice ever takes 
place on Arctic lowlands is explained by the observations of 
Lieut. Payer of the Austrian Polar Expedition, who found that 
during the short Arctic summer of the highest latitudes the ice- 
fields diminished four feet in thickness under the influence of the 
sun and wind. To replace this would require a precipitation of 
snow equivalent to about 45 inches of rain, an amount which 
rarely occurs in lowlands out of the tropics. In Siberia, within 
and near the Arctic circle, about six feet of snow covers the 
country all the winter and spring, and is not sensibly diminished 
by the powerful sun so long as northerly winds keep the air 
below the freezing-point and occasional snow-storms occur. But 
early in June the wind usually changes to southerly, probably the 
south-western anti-trades overcoming the northern inflow ; and 
under its influence the snow all disappears in a few days and the 
vegetable kingdom bursts into full luxuriance. This is very 
important as showing the impotence of mere sun-heat to get rid 
of a thick mass of snow so long as the air remains cold, while 
currents of warm air are in the highest degree effective. If, 
however, they are not of sufficiently high temperature or do not 
last long enough to melt the snow, they are likely to increase it, 
1 “ The general absence of recent marks of glacial action in Eastern 
Europe is well known; and the series of changes which have been so well 
traced and described by Prof. Szabo as occurring in those districts seems to 
leave no room for those periodical extensions of ‘ ice-caps ’ with which 
some authors in this country have amused themselves and their readers. 
Mr. Campbell, whose ability to recognise the physical evidence of glaciers 
will scarcely be questioned, finds quite the same absence of the proof o£ 
extensive ice-action in North America, westward of the meridian of 
Chicago.” (Prof. J. W. Judd in Geol. Mag. 1876, p. 535.) 
The same author notes the diminution of marks of ice-action on going 
eastward in the Alps ; and the Altai Mountains far in Central Asia show 
no signs of having been largely glaciated. West of the Kocky Mountains, 
however, in the Sierra Nevada and the coast ranges further north, signs 
of extensive old glaciers again appear ; all which phenomena are strikingly 
in accordance with the theory here advocated, of the absolute dependence 
of glaciation- on abundant rainfall and elevated snow-condensers and 
accumulators. 
