682 
PROFESSOR PRESTWICH ON THE ORIGIN 
Joseph Hooker* remarks on the low dome-shaped form of the ice in a basin several 
miles long and wide, high up in the Himalayas, which he refers to the meeting of 
tributary glaciers ; and Colonel God win-Austen describes a great glacier 2 miles wide, 
that receives a great number of tributaries, and along the centre of which stood a 
continuous line of huge masses of ice, which gives the idea they may have been 
squeezed up.t In the same way the old glaciers, meeting and clashing with a degree 
of antagonism unknown amongst modern glaciers, must often have expanded vertically 
or have been raised and piled up, in places, much beyond their normal height. J 
That such was the case in the Lochaber district there can be little doubt. We 
shall, in the next chapters, have to consider what may have been the effect of these 
obstructions to the normal flow of the ice-currents, not only in directing and massing 
the ice, but likewise in the distribution of the drift, including under that term the moraine 
deposits and the various beds of sand and gravel so widely spread over this district. 
§ 7. Exceptional Condition of the Ice-sheet in Lochaber. 
Bearing in mind the foregoing remarks, we will now show that, owing to peculiari¬ 
ties in the physiography of the Lochaber district, the condition of the great ice-sheet 
which there obtained must have been special and exceptional. Firstly, the Ben Nevis 
group being higher than any of the surrounding mountains, it would, cceteris paribus, 
give rise to glaciers larger and more powerful than those of the surrounding ranges. 
Secondly, the surface drainage from this group, instead of following the ordinary course 
from the centre to the sides, is directed to the northern side alone, so that there the 
valleys of the Spean and the Lochy received at the glacial period an excess of ice, as 
they now do of surface waters. For it will be observed that all the waters which 
run off the south side of the Nevis group flow into the two streams of the Nevis and of 
the Ileidh, which streams besides receive the drainage of the northern half of the 
parallel range of the Kilmallie mountains. The Nevis stream, which follows the course 
of Glen Nevis, after running several miles due west, turns suddenly northward, and 
debouches into the Great Caledonian Valley near where the Lochy joins Loch Linnhe. 
The Beiclh, also, on the same south side of this range, first runs some miles due 
east, and then joins at right angles Loch Treig, the course of which is north, and dis¬ 
charges into the Spean Valley. Lastly, owing to the position of the Ben Nevis group 
at the junction of the Spean and Lochy Valleys, its centralised ice-drainage was thrown 
on the lower reaches of these valleys, causing thereby an abnormal obstruction and 
accumulation of the ice at the entrance of Strath Spean and the Great Glen. 
* ‘ Himalayan Journals,’ vol. ii., p. 137. 
f “ On the Glaciers of Mustakh Range,” Journ. Roy. Geogr. Soc., vol. xxxiv., p. 40. Colonel Godwin- 
Austen informs me, however, that in his opinion the ice is forced up by underlying bosses of rock. 
+ In the Arctic Seas, ice floes, when squeezed together or driven ashore by strong winds or currents, 
pile up to great heights. 
