The Parallel Roads of GIol Roy. — Upliani. 297 
where the highest shore terminates. The maximum depth of 
the lake in this stage, east of Bohuntine hill, ^^^s 650' feet. 
Its width in the Glen Roy was mainly between a half and 
three-fourths of a mile, and it was only slightly diminished in 
width along this mountain valley by sinking to the later and 
lower shores. 
When the ice-sheet, in its general southwestward recession 
from' this mountainous region, laid bare the col at the head of 
Glen Glaster, leading into the Spean valley, lake Roy was 
lowered to that pass. P'or a short time, perhaps a few years, 
this new outflow was stationary at a level of about 1,100 feet, 
shown by a faint shore mark seen along a distance of about 
two-thirds of a mile where the Roy valley bends northeast of 
the Turret bridge. Winds blowing through the valley had a 
longer stretch of the lake for raising its waves there than on 
any other part of it's shores. Elsewhere this beach line is 
wanting or scarcely observable. 
The Glaster col has an altitude of 1,075 ^^et, being filled up 
with peat several feet above its original hight. Its belt of 
shore erosion, constituting the middle one of the Parallel 
Roads, lies between upper and lower limits of 1,077 and 1,062 
feet. The lake surface was nearly at 1,070 feet, with wave 
wearing in storms above and beneath that level. The earliest 
outflow in the Glaster pass may have been upon its northeast 
side about 30 feet above the central depression which was soon 
afterw^ard occupied when permitted by slightly farther retreat 
of the ice. Or a barrier of glacial drift about 30 feet high 
may at first have obstructed the valley close southeast of the 
later col, where now such drift deposits partly remain, facing 
the brooklet with steeply undercut front. 
During the formation of the Glaster shore line the lake 
extended about a mile farther down Glen Roy, and into Glen 
Collarig over the pass north of Bohuntine hill, than at its 
earlier highest stage. Its maximum depth, at the lowest point 
to which it extended, was nearly the same as before. 
With the recession of the ice-sheet only one mile and a 
half southward from Glen Glaster, around the west side of 
Creag Dhubh, lake Roy spread into the Spean valley and fell 
about 215 feet more, to the level of the col east of loch Lag- 
gan, between the Spean and Spey valleys. This col has a 
