OF THE PARALLEL ROADS OF LOCHABER. 
667 
the Spean, and resting on Moeldhu which is opposite, shut up the lower end of Strath 
Spean ; while a third glacier issued from Glen Treig, and barred the valley of the 
Spean higher up. The last two glaciers served as barriers to the Glen Roy lakes, 
all of which he considered had extended into the opposite part of Glen Spean. On 
the retreat of the glacier of Glen Treig, the lake-waters were lowered, and, spreading 
into upper Glen Spean, escaped eastward through Glen Spey. In proof of the exist¬ 
ence of this glacier, Agassiz pointed out that the striae on the rocks in Glen Spean, 
opposite Glen Treig, were parallel with the axis of Glen Treig and transverse to the 
direction of Strath Spean. But his allusion to the phenomena of the parallel roads 
was incidental to the general question, and the subject was not discussed in detail. 
Adopting the glacial theory and general views of Agassiz, Mr. Jamieson, in 1863, 
with an intimate knowledge of the drift phenomena of the north of Scotland, sought, 
in a further investigation of the district, for the more special conditions applicable to 
this particular case.'”' 
Scotch geologists had in the meantime come to the opinion that the first great 
glaciation of the country had been succeeded by a warm interglacial period, which was 
followed by another period of considerable cold, during which only local glaciers 
descended from the greater mountain ranges. 
Mr. Jamieson concluded (although apparently with some hesitation) that it was 
during this latter period t that the lakes of the Lochaber district originated. He also, 
like Agassiz, attributes then’ formation mainly to two great glaciers, but differently 
disposed. One issuing from Glen Arkaig, and crossing the Great Glen,—at that time 
probably filled with ice from its summit level at Loch Oich to Fort William,—closed 
Glen Gluoy, and then flowed with the main stream over the shoulder of Strone-y-Vaa 
to near Tiendrish. Whence he concluded (p. 246), “ that the Glen Arkaig glacier not 
only blocked up Glen Gluoy, but also largely contributed to close the mouth of Glen 
Spean”—aided on the opposite side by a glacier from Coire n Eoin. 
The other glacier issuing from Glen Treig, “ and protruding across Glen Spean until 
it rested on the hills upon the north side of that valley,” blocked up the pass of Glen 
Glaster, while one main stream, turning westward, extended to the entrance of Glen 
Boy, where it served to dam the Glen Boy lake during its two higher levels, and 
another passed up the Spean Valley and through the pass of Makoul into the basin 
of the Spey. “ This,” he observes, “ would cut off all outlet to the eastward, both by 
Glen Glaster and Makoul, and, so long as the icy barriers maintained a sufficient 
* “ On the Parallel Roads of Glen Roy, and their Place in the History of the Glacial Pei’iod,” Quart. 
Journ. Geol. Soc., vol. xix., p. 235, 1863. See also Mr. Jamieson’s “ Ice-worn Rocks of Scotland,” Ibid., 
vol. xviii., p. 164, 1862; “ History of the last Geological Changes in Scotland,” Ibid., vol. xxi., p. 161, 
1865 ; and “ Last Stage of the Glacial Period in Great Britain,” Ibid., vol. xxx., p. 328, 1874. 
t Sir Chaeles Lyell, who adopted the hypothesis of Mr. Jamieson, was of opinion not only that the 
lakes were formed in times long subsequent to the principal glaciation of Scotland, but also that they 
might have been as late, especially the lowest one, as that portion of the Pleistocene period in which Man 
coexisted with the Mammoth.—‘Antiquity of Man,’ 4th edit, p. 312. 
