712 
PROFESSOR PRESTWICK OK THE ORIGIN 
apparently, not on the other side), just where the barrier stood. This absence of the 
lines on the site of a barrier is to be noticed also on the sites of the presumed minor 
barriers in the passes of Glen Roy and Glen Glaster. 
§ 14. The “ Main Barriers ” at the Entrance of the Glens. 
The main barriers to Glen Gluoy, Glen Roy, and Glen Spean were, I consider, as 
before stated, mainly due to the circumstance of an accumulation of ice so excessive 
as to last for a certain time after the ice generally had greatly given way. This limits 
the time for the formation of the “ roads,” as such ice-barriers, under these conditions, 
could not have had a very long duration. The formation of the “ roads ” on the hypo¬ 
thesis advanced in this paper is not, however, dependent on great length of time. 
Of the barrier to Glen Gluoy I am not able to speak further (ante, p. 683). With 
respect to the Glen Roy barrier, although it may have consisted chiefly of ice, it 
evidently was formed in considerable part of moraine detritus, brought on the one 
side by the glacier coming down Glen Roy, and on the other by the ice from the Ben 
Nevis range and the Spean Valley. Meeting here in opposition, not only were the ice- 
streams checked and heaped up, but the moraine detritus was also massed and spread 
over the bottom of the glen, forming a bed extending from a short distance beyond the 
entrance of Glen Glaster to and beyond Bohuntine. So important was this deposit 
of moraine matter, that the portion of it which remains, after the bursting of the 
barrier and the long-continued abrasion of the river, still forms a continuous mass 
2 miles or more in length and from 50 to 200 feet or more thick, rising from the bed 
of the valley (which is, where the deposit is thickest, 350 feet above the sea) to the 
height of 700 to 750 feet on the slope of Bohuntine Hill, or to within 100 feet or less 
of the level of the lower “ road” No. 4. On the opposite side of the river much less 
seems to remain. Considerable remnants of moraine detritus, overspread with a large 
amount of its water-worn and iron-stained debris, also extend to Auchaderry and Roy 
Bridge. The following is a section of the valley on the line of the barrier. 
Fig. 18. 
§» 
W § £ 
i 
Diagram section across Glen Roy, 1 mile N. of Boliuntine: distance across on No. 2 line—1 mile nearly. 
b. Moraine deti’itus and gravel. I am uncertain of its extent on tlie east side of the section. 
Mr. Milne Home describes another important mass in Glen Collarig, where the 
