1875.] Niagara. 145 
and it could not fail to be so, for to the land it occupied the 
position of a great valley, down which the ice from the north 
would naturally flow. I do not think, however, that the 
time of the greatest extent of ice in the sea-bed was the 
same as that of the greatest thickness of ice on the land; 
for, as the margin of the ice of the ocean-bed moved south- 
ward, it would cut off the moisture-bearing currents tra- 
velling towards the land, and gather to itself the precipita- 
tion from them. ‘Thus, I think it was that the ice on the 
land shrunk back, at the time of the greatest extent of that 
which occupied the bed of the Atlantic; and we have, both 
in America and Europe, a period of land-ice, followed by 
one of fresh-water deposits and fresh-water borne ice- 
bergs. 
I endeavoured to show in my paper, published in this 
journal in Oétober last, that the ice from Greenland also 
reached the western coast of Europe. It passed across Ice- 
land, and overflowed Caithness. Iceland is so hugely gla- 
ciated, that we may conclude the northern ice invaded it 
also; and, extreme as the view may seem, I can find no 
other satisfactory explanation of the fact, that the whole of 
the south of England is mantled by fresh-water glacial 
beds, than on the supposition that, at the height of the 
glacial period, the English Channel was blocked up to the 
south-west by ice that extended in an unbroken mass from 
Greenland. I sought in vain, before my last visit to North 
America, for a satisfactory solution of the presence of the 
fresh-water gravels and floated boulders of the south of 
England, and was driven to suppose that one or more bar- 
riers of land must have existed in the western part of 
the British Channel; but, after seeing how the ice in the 
bed of the Atlantic blocked up the water-shed of the eastern 
seaboard of North America, ten degrees of latitude further 
south, I have no difficulty in imagining that it may also 
have blocked up the English Channel, and caused the for- 
mation of the high and low-level gravels, the beds of the 
Rhine, and the floated boulders of Devonshire, Somerset- 
shire, and Wales. I venture to predict, that evidence will 
yet be found of the encroachment of the edge of this ice 
from the north-west upon the Continent, probably upon the 
coast near Brest, and I also expect that traces will be dis- 
covered of the great flow of water that must have taken place, 
either round the south-eastern termination of the ice, or 
around the mountains of Britany, into the valley of the 
Loire. 
