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334 T. E. JAMIESON ON THE LAST STAGE OF
of snow would be melted before the ice in the central trough of the
valley broke up, so that heavy floods of turbid water would be let loose
over the surface of the frozen rivers and thus rise to great heights
along their banks. The thick solid ice occupying the bed of the
stream would take longer to melt, but would gradually break up,
rising to the surface in great masses, and bringing with it stones and
pebbles from the bottom. These masses of ice would float down the
stream, dropping the boulders here and there as they dissolved.
"When the Straits of Dover were dry land and the rivers wandered
away down far below the present coast-line, it is probable that during
the winter season the Seine, the Somme, the Thames, &c. would be
completely frozen along what are now the lower reaches of these
rivers, and at the break up of the snow in summer these frozen
masses would cause the river-floods to rise to heights which now
appear very marvellous.
Mr. Prestwich has discussed this subject in an excellent manner
in the «  Philosophical Transactions ' for 1864, p. 286

and I would
only suggest that he has perhaps not sufficiently allowed for the
unmelted ice in the bottom of the valley, forcing the floods to reach
a height they could not otherwise do.
The underground ice of Siberia may have been buried in this way
by the rivers flooding it and flinging down beds of mud on it before
it had time to melt and become detached from the bottom.
§ 8. Comparative Olaciation of East and West Coasts.
I have often been struck with the remarkable intensity of the
glacial action displayed on the rocks of the west side of Scotland
compared with the east, and in a former paper

I threw out the
suggestion that the precipitation of snow along the west Highlands
had probably much exceeded what fell on the eastern slope of the
island, just as takes place now in regard to the rainfall. Thanks to
the Meteorological Society of Scotland, we have now accurate data
concerning the rain

and Mr. Buchan's excellent papers on the
subject show us what an immense excess there is in the quantity
that falls on the west side of the country compared with the east.
There are several stations in the west Highlands where the annual
rainfall exceeds 100 inches, whereas along the east coast it ranges
generally from 25 to 30

and it is interesting to note that the gla-
ciation of the rocks corresponds in intensity with the present excess
of the rainfall, showing that the precipitation of snow had been
similarly distributed

and is it not the case generally that the marks
of ancient glaciers are most decided where the rainfall is now
heaviest ?
The prevailing wind in Scotland is the south-west, which, sweeping
up the moisture from the Atlantic, is cooled as it rises over the
mountain-tops of the west coast and throws down its burden in
copious showers on those hills, so that before it reaches the eastern
side of the island it is a comparatively dry wind. Tbis is well seen

Quart. Journ. Geol. Soc. xix. p. 258,