498 Proceedings of Societies . [July, 
2nd. In consequence of the lowering and partial submergence 
of the land, and its conversion from a continental area to an 
archipelago, combined possibly with some other more general 
cause, an amelioration of the climate took place, attended by a 
gradual melting of the ice-sheet in all the lower traCts. The 
snow and ice wasted from the valleys and from the lower moun- 
tain summits, and, in the absence of any established water- 
courses, the hollows and depressions in the ice, when not 
fissured, were converted into pools and tarns, until the continued 
liquefaction opened out surface channels or interior fissures, by 
which the water could ultimately escape. 
3rd. That pending the establishment of natural lines of 
drainage, and in presence at places of unusual obstruction, the 
water accumulated in some valleys in larger bodies or lakes ; and 
if in those cases, the mouth of the valleys being closed by the 
main ice-barriers, other channels of escape — such as cols or 
passes — communicating with adjacent glens or valleys presented 
themselves, the water overflowed through these channels as soon 
as it rose to the height of such cols or passes. Or should the 
cols have been also barred by ice, that ice would have given way 
as soon as the increasing height and pressure of the water proved 
sufficient. When this happened the water would at once fall to 
the fixed level regulated by the col, and thus no record, such as 
we have in Lochaber, might be left of the presence of the ori- 
ginal bodies of water. 
4th. In the Lochaber district, while the exceptional accumu- 
lation of ice in the Spean Valley barred the entrance of the glens 
on the north side of that valley, their passes were also blocked 
by remnants of the great ice-sheet ; and the formation of the 
detrital shelves is due to the sudden bursting of these minor 
barriers, when the waters of the lake were discharged with great 
rapidity, until they fell to the level of the col. Under these cir- 
cumstances the mass of loose debris covering the hill sides 
below the line of water-level gave way, and slid atter the 
retreating waters, until stayed with greater or lesser abruptness, 
according to the angle of slope and the volume of the mass, on 
the discharge ceasing and the waters coming to rest. The 
shelves so formed, modified slightly by subsequent subaerial 
aCtion, constitute the “ roads.” 
5th. The moraine detritus in places where the glaciers clashed, 
and where their progress consequently became checked or de- 
layed, tended also to accumulate or heap up, and in this way in 
the Lochaber glens added to the strength and permanence of the 
ice-barriers. 
6th. While the moraine detritus was irregularly distributed 
under the ice, or massed in particular places, the debris projected 
on the surface of the ice-stream, and contained in its body, was 
either left in situ on its liquefaction or else was — as the result of 
the great floods consequent upon the bursting of lake barriers— 
