62 
THE PARALLEL ROADS OF 
Prepossessed as I was with the idea of 
glacial agency in times anterior to ours, these 
of the valley of the Spean, as well as that of Glen Roy, is 
occupied by loose materials, partly drift, that is, materials 
acted upon by glaciers, and partly decomposed fragments of 
rocks brought down by the torrents, greatly impeding the 
observation of the polished surfaces. The river-bed is cut 
through this deposit, and here and there through the under¬ 
lying rock. Besides the parallel roads, there are also peculiar 
accumulations of loose materials in Glen Roy and Glen Spean, 
more particularly connected with the lowest terrace, which 
Mr. Darwin and Professor Jamieson have shown to be little 
deltas formed during the existence of the lake of Glen Roy at 
the bottom of the gullies intersecting the shelves of the upper 
roads. The outlet for the water at the period during wdiich 
the second terrace was formed, not known when I visited 
Glen Roy, has been discovered by Mr. Milne-Holme, and 
also observed by Professor Jamieson. During the formation 
of the upper terrace the waters escaped through the western¬ 
most tributary of the river Spean, in the direction of the 
northeast corner of the woodcut, and during that of the 
lowest terrace, at the eastern end of Loch Laggan, also 
through the valley of the Spean. The state of preservation 
of the parallel roads is such as to prove that no disturbance 
of any importance can have taken place in the country since 
they were formed. Far from believing, therefore, that these 
remarkable shelves are ancient sea-beaches, I am prepared to 
maintain that, had the area occupied by them been sub¬ 
merged only for a few days, under an ocean rising and falling 
for several feet with every tide, no vestige would have been 
left of their former existence. 
