GEOLOGY. 
75 
the inquiry into the traces of a comparatively recent cold period in the 
earth’s history. Closely connected with this inquiry is the equally im¬ 
portant question as to the former occurrence of similar glacial epochs at 
regular or irregular intervals of geological time. 
The evidence of the last glacial epoch may be traced in two ways— 
by the form of the surface, which has been modified by the action ol 
ice, and by changes that have taken place in the fauna and flora of the 
country in consequence of the alteration in the climate. The effects of an 
ice-sheet, like that now occurring in Greenland, if such formerly existed 
in comparatively low latitudes, must have been to round off, score and 
polish the rocks of the country in a peculiar manner, easily recog¬ 
nised by those familiar with glaciated areas.* Glaciers, properly so 
called, are confined to hilly or mountainous countries, and the valleys 
formerly occupied by them retain more or less the form of the letter U 
instead of taking the shape of the letter V, as they do when they have 
been cut out by running water. The sides of the valley, when modified 
by a glacier, have a tendency to assume the form of slopes unbroken 
by ravines, and with all ridges planed away or rounded, whilst in ordinary 
valleys of erosion by water, the sides consist of a series of side valleys or 
ravines, divided from each other by sharp ridges running down to the 
main valley. Large and small masses of rock, preserving to a considerable 
extent an angular form, but frequently polished and grooved by being 
ground against the sides or bottom of the valley, are carried down by the 
ice, and either left behind, perched up high on the slopes of the valley, or 
accumulated in a vast heap or bank, known as a terminal moraine, at the 
spot where the ice has terminated. The nature of the rock will usually 
show whether the fragments on the side of a hill or at the bottom of a 
valley are derived from the higher parts of the drainage area, or whether 
they have merely fallen down from the neighbouring slopes. In the latter 
case, they may be due to landslips; in the former, their shape and the 
erosion they have undergone will aid in showing whether they have been 
transported by water or ice. 
The surfaces that have been modified by earlier glacial epochs must 
* Care should be taken that the peculiar scoring and grooving of rock surfaces 
produced by the action of sand transported by the wind be not mistaken for 
glacial evidence. 
