54 
THE PARALLEL ROADS OF 
ice, during the glacier-period, overtopped nearly 
all the mountains, so that few fragments could 
fall from them upon its surface, we find scarcely 
any angular boulders, while the drift is inter¬ 
spersed with larger fragments of this charac¬ 
ter, carried under the ice, instead of on its 
hack. Another distinction between water- 
worn deposits and drift consists in the fact 
that the former are washed clean, while the 
latter always retains the mud gathered during 
its journey and spread throughout its mass. 
In summing up the glacial evidences, I must 
not omit the moraines, though I have described 
them so fully in a previous chapter that I need 
not do more than allude to them here ; but any 
argument for the glacial theory which did not 
include these characteristic walls erected by 
glaciers would he most imperfect. We need 
hardly discuss the theory of currents with 
reference to the formation of terminal mo¬ 
raines, extending across the valleys from side 
to side. Any current powerful enough to 
bring the boulders and debris of all sorts of 
which these walls are composed to the places 
where they are found would certainly not build 
them up with such regularity, but would sweep 
