TJie Parallel Roads of Glen Roy. — Uphain. 299 
of lake Roy, perhaps no more than one or two centuries for 
all its stages together. About a third part of its whole time 
of existence, represented by the formation of the Glaster shore 
line, elapsed during a retreat of the ice border across a dis- 
tance of less than two miles. 
Lake Gloy, which attained a length of about six miles, 
with a width of one-fourth to three-fourths of a mile and a 
maximum depth of abovit 700 feet, overflowed from Glen Gloy 
into the Chomhlain and Turret arm of Glen Roy. The col is 
1. 172 feet above the sea, but it is filled up about six feet with 
peat. The Gloy shore erosion lies between vertical limits of 
1.173 ^"^^^ I > 1^56 feet, the surface of the lake having been at 
1,166 feet, very nearly. Its single shore line is, I think, more 
conspicuous than eitlier of the Glen Roy Roads. The out- 
flowing stream, during the highest stage of lake Roy, had a 
descent of about 16 feet and a length of perhaps a third of a 
mile 
Both these glacial lakes were brought to an end by the 
southwestward retreat of the ice, when it opened the Gloy 
and Spean valleys to the area of loch I.ochy in the Great Glen 
of Scotland. Although that deeper and broader, nearly 
straight glen or valley was still filled by the fast waning ice- 
sheet on the southwest, it was wholly open northeastward past 
loch Ness to the sea. Its present watershed has an altitude 
imly slightly exceeding 100 feet, across which the ice-held 
lakes of the Gloy, Roy, and Spean valleys were plainly drained 
away. 
Excellent opportunity to trace the old shore lines is 
afforded bv the absence of trees or even bushes from nearly 
all the country. lUit in many places the stumps and roots of 
trees were observed in the peaty soil, where any rivulet had 
cut to a slight depth. The destruction of the former groves 
and woods liere seems probably attributable to their use for 
fuel, as in some almost entirely prairie areas of the u])])er 
Mississippi basin. 
Deltas of very small volume were Ijrought into lake Roy 
in its successive stages by several of its tributaries. All these 
streams are short, and they had only a brief time for this work 
during the existence of the glacial lake. Their later alluvium 
carried into the glen is of far greater volume, as notablv in 
