104 GLACIAL PHENOMENA IN MAINE. 
lire; the characteristic markings, furrowing, 
grooving, scratching, and polishing of the sur¬ 
faces over which the glacier passed, as well as 
of the pebbles and stones held fast in its mass, 
and coming into sharp contact with the rocks 
beneath; the accumulation of loose materials 
pushed along by the advancing ice, or carried 
on its edges, and forming ridges or walls at 
its terminus and on its sides. The study of 
these combined results of glacial action now be¬ 
came part of the subject, and were sought for 
by geologists wherever the erratic phenomena 
were investigated. Out of these comparisons 
has gradually grown a belief that, as the 
Alpine glaciers were formerly more extensive, 
so did the northern ice-fields, now confined to 
the Arctic regions, once stretch farther south. 
I suppose there are few geologists now who 
would not readily give their assent to the 
glacial theory, expressed in this general form. 
But while the 1 wider distribution of glacial 
phenomena from mountainous centres in an¬ 
cient times is now generally admitted, the 
theory in its more universal application, in¬ 
volving, that is, the existence of an ice-slieet 
many thousands of feet in thickness moving 
