52 
THE PARALLEL ROADS OF 
pardoned for dwelling upon this point, because 
the great controversy among geologists respect- 
ing the nature and origin of the sheet of loose 
materials scattered over a great part of the 
globe turns upon it. The debris of which the 
drift consists are thrown together pell-mell, 
without any arrangement according to size or 
weight, larger and smaller fragments being 
mixed so indiscriminately that the heaviest 
materials may be on the very summit of the 
mass, and the lightest at the bottom in imme¬ 
diate contact with the underlying rock, or the 
larger pieces may stand at any level in the 
mass of finer ones. Impalpable powder, coarse 
sand, rounded, polished, and scratched frag¬ 
ments of every size, are mixed together in a 
homogeneous paste, in which the larger mate¬ 
rials are imbedded, to use a homely but ex¬ 
pressive comparison, like raisins and currants 
in a pudding. The adhesive paste holding all 
these fragments together is, no doubt, the re¬ 
sult of the friction to which the whole was 
subjected under the glacier, and which has 
worked some of the softer materials into a 
kind of cement. 
The mode of aggregation of water-worn ma- 
