OF THE PARALLEL ROADS OF LOCHABER. 
683 
On the north of these mountains, the glaciation of Larig Leacan and of Coire ’n 
Eoin shows the descent of glaciers down those glens, and others no doubt descended 
Glens Diombadh and Mhuilinn, and the other smaller glens on the flanks of this range 
from Ben Nevis to Loch Treig. It will be observed that all these glens rise amongst 
the higher summits of the district, that their gradients are steep, and that glaciers 
projecting from them would, after crossing the Spean Valley, tend to mass (or force 
the Spean stream to mass) against the opposite range of hills between Glen Boy and 
Loch Lochy, and on the hills at the entrance of the Great Glen. 
Besides these, the great glaciers coming down Glen Treig and Glen Nevis threw 
into the valley of the Spean and of the Lochy large masses of ice flanking the foregoing 
central glaciers of the group, so that a barrier was thus raised to the descent of 
the ice-stream from the upper part of the Spean Valley above Glen Treig, while the 
great glaciers debouching from Glen Eil and other lateral valleys into Loch Linnhe 
blocked up the western outlet of the Spean and Lochy ice. This mass of ice seems 
therefore to have been diverted northward and eastward, where the resistance was less, 
one portion taking a direction along the Great Glen, and another passing over the water¬ 
shed of the Spean and down the valley of the Spey. The obstacles to this course are 
not so formidable as might at first sight appear, for the bed of the Spean A"alley, to 
where it is joined by Glen Treig, only falls about 200 feet below the level of the pass 
of Makoul, over which the ice-stream of the upper tributaries passed, while the water¬ 
shed of the Caledonian valley rises only to the height of 94 feet. It is a question, 
also, which we shall afterwards consider, whether the Ben Nevis range did not stand 
relatively higher then than now to the east coast, so that the eastward gradients were 
greater, or possibly in the Caledonian Glen were even continuous throughout. 
The western portion of the great body of ice in the Spean and Lochy Valleys, 
diverted therefore in a direction north-east along the Caledonian Valley by the block 
before alluded to, met the glaciers issuing at right angles from Glen Loy, Glen Arkaig, 
and others on the north side of the river Lochy and of the loch of that name, and was 
thus driven to hug the hills on the opposite side of the Great Glen— i.e., those at the 
entrance to Glen Spean and Glen Gluoy, massing in them front and moving up the 
tributary valleys where there was no counterbalancing resistance, or until checked 
by the local ice already in occupation of those valleys. 
It appears certain that in consequence of the physical conditions just named, the 
accumulation of ice caused by the conflicting and opposing currents, and by the block 
which ensued, must have attained exceptional proportions at the entrance of the 
Lochy, Spean, Boy, and Gluoy Valleys, and thus formed barriers to these valleys of 
great height and dimensions. 
The direction of the strise noted by Mr. Jamieson near Strone-y-Vaa and at Black- 
letter I take to be due, not to an incurrent ice-stream from Glen Arkaig, but to an 
excurrent stream passing out from the lower part of the Spean Valley into the Great 
Glen; and, in the same way, the strife at the entrance of and in Glen Gluoy are due to 
