212 
THE FORMATION OF GLACIERS. 
to contain the traces of animals whose presence 
indicates a climate many degrees colder than that 
now prevailing there. 
But these organic remains are not the only evi- 
dence of the geological winter. There are a num- 
ber of phenomena indicating that during this 
period two vast caps of ice stretched from the 
Northern pole southward and from the Southern 
pole northward, extending in each case far tow- 
ard the Equator, — and that ice-fields, such as 
now spread over the Arctics, covered a great part 
of the Temperate Zones, while the line of perpet- 
ual ice and snow in the tropical mountain-ranges 
descended far below its present limits. As the 
explanation of these facts lias been drawn from 
the study of glacial action, I shall devote this and 
subsequent articles to some account of glaciers 
and of the phenomena connected with them. 
The first essential condition for the formation 
of glaciers in mountain-ranges is the shape of 
their valleys. Glaciers are by no means in pro- 
portion to the height and extent of mountains. 
There are many mountain-chains as high or high- 
er than the Alps, which can boast of but few and 
small glaciers, if, indeed, they have any. In the 
Andes, the Rocky Mountains, the Pyrenees, the 
Caucasus, the few glaciers remaining from the 
great ice-period are insignificant in size. The 
volcanic, cone-like shape of the Andes gives in- 
