62 
PROCEEDINGS OE SOCIETIES. 
their own previous deposits. But this formation exists in situations far 
removed from any rivers, and it often forms the subsoil of our higher 
lands. In the limestone country its boulders and gravel are chiefly lime¬ 
stone ; hut it contains in a greater proportion than the escars a mixture 
of Silurian and other sandstones, mica slates, greenstones, and sometimes 
granite; and indeed it is, probably, from the decomposition of those 
rocks that the blue and yellow clays which it contains are derived. The 
greater part of these beds and accumulations may have been originally 
deposited as boulder drift, and afterwards disturbed and mixed with new 
matter at the escar period. To the escar movement may be attributed 
the deeper soils and superior fertility of our greater hills on the north 
than on the south side. 
Having explained my opinions, and the reasons on which they are 
founded, regarding the proper separation of our drifts into three great 
divisions, the places they occupy in relative position, and the directions 
in which they moved, I will now state my views as to what the force 
may have been by which those remarkable effects were produced. Two 
theories have been proposed,—one of which would make water the mov¬ 
ing agent, and the other ice. The latter is the latest, and has the re¬ 
commendation of novelty in its favour, besides the more substantial one 
of being the adopted of Agassiz. 
It may be with the geologist as with the painter or the musician, 
in whose works, though they speak the universal language of genius, a 
national accent can still be noticed; and the ice or water theories may, 
to a great extent, owe their origin to the physical circumstances of the 
native countries of their proposers. An inhabitant of Switzerland who 
has been accustomed to observe the vast power of the glaciers grinding 
away the sides of mountains, scooping out their bed in the granite rock, 
and carrying the fragments of fallen peaks on the crests of their solid 
waves, must see that ice is indeed a great agent in geological pheno¬ 
mena ; and, on the other hand, to a native of our western isles who has 
been viewing the Atlantic from his childhood, and has seen cliffs pulled 
down, and the huge masses of their debris tossed about by the surge, 
the force of water will be considered unsurpassed. One, as correctly as 
the other, might found a theory of limited applicability on the great 
power that he had been used to contemplate; but they would be equally 
wrong in seeking to give it too great a generalization. 
I believe that Agassiz, though not the inventor of the glacial hypo¬ 
thesis, was the first who conjectured the former existence of glaciers in 
the British Islands, and it would be far from me to question the correct¬ 
ness of that great man’s opinion, supported as it has been by our own 
most eminent geologists ; but in the district to which this paper refers 
I believe that it is neither to land glaciers nor floating ice, but simply 
to the moving force of water, that we must attribute the phenomena of 
drift. 
Nothing can be more marked than the increase in number, as well 
as in size and angularity, of our boulders as they are followed to their 
source; and my knowledge of that fact has often assisted me in tracing 
