168 
ELEMENTS OF GEOLOGY. 
as we travel towards the Arctic regions. They could not 
tail to be struck with the contrast which the countries bor¬ 
dering the Baltic presented when compared with those sur¬ 
rounding the Mediterranean. The multitude of travelled 
blocks and striated rocks in the one region, and the absence 
of such appearances in the other, were too obvious to be over¬ 
looked. Even the great development of the boulder forma¬ 
tion, with large erratics so far south as the Alps, offered an 
exception to the general rule favorable to the hypothesis 
that there was some intimate connection between it and ac¬ 
cumulations of snow and ice. 
Transporting and abrading Power of Glaciers. — I have de¬ 
scribed elsewhere (“Principles,” vol. i., chap, xvi., 1867) the 
manner in which the snow of the Alpine heights is prevent¬ 
ed from accumulating indefinitely in thickness by the con¬ 
stant descent of a large portion of it by gravitation. Be¬ 
coming converted into ice it forms what are termed glaciers, 
which glide down the principal valleys. On their surface 
are seen mounds of rubbish or large heaps of sand and mud, 
Fig. 106. 
Limestone, polished, furrowed, and scratched by the glacier of Kosenlau in 
Switzerland. (Agassiz.) 
a a. White streaks or scratches, caused by small grains of flint frozen into the ice. 
hh. Furrows. 
* 
with angular fragments of rock which fall from the steep 
slopes or precipices bounding the glaciers. When a glacier, 
