680 
PROFESSOR PRESTWICH ON THE ORIGIN 
rounded, while above, at m, are heaps of coarse moraine detritus. Fig. 5 is an outline 
section : the rounded rock surfaces r extend apparently to about the level a. 
Fig. 5. w. 
m 
Outline section of tlie ravine at entrance of Glen Larig Leacan. 
The “ erratic blocks” so abundant over this district furnish additional evidence of 
the height and direction of the ice-sheet, though as yet only a limited number have 
had their exact position and origin determined.* 
Mr. Darwin found granite boulders on the hills between Glen Roy and Glen 
Gluoy, at heights of 1,600 to 1,700 and 2,200 feet; on Meal-Dubh above 972 feet; 
in the Gap of Collarig on and about the upper terraces (“ roads ”) ; in the valley of 
Glen Roy; and on the side of Tombrahn.t He considered that they may have been 
derived from the granite hills near the source of the Roy. 
Mr. Milne Home j found transported boulders on Bohuntine Hill at 800 to 1,100 
feet; at the head of Glen Glaster at 1,000 to 1,200 feet; and at the head of Glen 
Roy at 1,320 feet. He also states that thick beds of sand and gravel occur on the 
hills around Glen Gluoy at heights of from 1,700 to 1,800 feet; on Ben Chlinaig 
at 1,700 feet; and on the hill N.E. of Rough Burn at 1,700 feet. Mr. Milne Home, 
however, attributes these and other blocks and drift beds to floating ice, carried from 
the W. and W.N.W., and to marine action. 
Mr. Jamieson found near the summit of Craig Dhu (2,161 feet), and on the top of 
Bohuntine Hill (1,750 feet),§ transported boulders of a “ syenitic granite,” wdiich he 
traces to rocks of this character in the valley of the Spean opposite Glen Treig. He 
traced other boulders of the same rock up the valley as far as Makoul. 
* The Boulder Committee of the Royal Society of Edinburgh is collecting valuable data relating to 
this subject—data essential to settle definitely the question of transport of these blocks by land or sea ice. 
f Mr. Darwin takes the heights of the “roads” given by Macculloch, which, as he suspected, have 
been found to be about 100 feet too high, so a correction to this extent has to be applied to these and 
some other heights given in his paper.— Op. cit., p. 68. 
J Trans. Roy. Soc. Edinb., vol. xxviii., p. 640. 
§ Quart. Journ. Geol. Soc., vol. xviii., pp. 174-176, 
