out by observations at the two ends
of the Caledonian Canal. Fort William at the south-western end has,
as just stated, 86 inches, while Culloden, at its north-eastern end,
has only 24. To the researches of that able and accomplished
meteorologist, Mr. Buchan, we are indebted for these and other data of
the most interesting and valuable kind.

Adhering to the facts now presented to us, it is not difficult to
restore in idea the process by which the glaciers of Lochaber were
produced and the glens dammed by ice. When the cold of the glacial
epoch began to invade the Scottish hills, the sun at the same time
acting with sufficient power upon the tropical ocean, the vapours
raised and drifted on to these 'northern mountains were more and more
converted into snow. This slid down the slopes, and from every
valley, strath, and corry, south of Glen Spean, glaciers were poured
into that glen. The two great factors here brought into play are the
nutrition of the glaciers by the frozen material above, and their
consumption in the milder air below. For a period supply exceeded
consumption, and the ice extended, filling Glen Spean to an
ever-increasing height, and abutting against the mountains to the
north of that glen. But why, it may be asked, should the valleys
south of Glen Spean be receptacles of ice at a time when those north
of it were receptacles of water? The answer is to be found in the
position and the greater elevation of the mountains south of Glen
Spean. They first received the loads of moisture carried by the
Atlantic winds, and not until they had been in part dried, and also
warmed by the liberation of their latent heat, did these winds touch
the hills north of the Glen.

An instructive observation bearing upon this point is here to be
noted. Had our visit been in the winter we should have found all the
mountains covered; had it been in the summer we should have found the
snow all gone. But happily it was at a season when the aspect of the
mountains north and south of Glen Spean exhibited their relative
powers as snow collectors. Scanning the former hills from many points
of view, we were hardly able to detect a fleck of snow, while heavy
swaths and patches loaded the latter. Were the glacial epoch to
return, the relation indicated by this observation would cause Glen
Spean to be filled with glaciers from the south, while the hills and
valleys on the north, visited by warmer and drier winds, would rem