1863.] JAMIESON — PARALLEL ROADS OF GLEN ROY. 251 



rivulets sufficient to account for this. As far as I remember, there 

 is an absence of delta-matter in Glen Turrit at the level of the two 

 upper lines. Perhaps this may be explained by remembering that 

 the two upper lines mark severer glacial conditions, when the hills 

 would be more covered with snow, and perhaps abound less in 

 running water. Glen Gluoy, as I have said, might then be filled 

 with snow and ice; consequently there would be no lake discharging 

 into Glen Turrit, and hence no delta-matter. Hence also the fainter 

 mark of the Glen Gluoy line. 



Glen Gluoy and Glen Eoy are both very narrow glens, not having 

 basins fitted for feeding glaciers ; it is probable, however, that, at 

 the upper extremity of the latter, traces of glaciers may be found 

 interrupting the mark of the highest line, but circumstances pre- 

 vented me from examining that locality properly. 



Mr. Darwin, in his memoir, alludes to some horizontal mounds or 

 patches of earthy matter near the cols, and at a higher level. Mr. 

 Robert Chambers also lays much stress on certain horizontal markings 

 in Glen Spean, above any of the Parallel Roads. Some of these I ob- 

 served. An instance of such is distinctly seen high up on the front 

 of Ben Chlinaig when viewed from Bohuntine. I, however, ascer- 

 tained that these short lines on Ben Chlinaig were neither quite 

 horizontal nor perfectly parallel. I therefore think they have arisen 

 from some other cause than what formed the roads of Glen Roy. I 

 am of opinion that many of these cases are connected with that 

 former great extension of the ice which preceded the period of the 

 Roads. They may mark the edge of those great ice-fields that for- 

 merly filled the valleys, being either lines of moraine matter or stuff 

 accumulated in lateral pools between the ice and the hill-sides. These 

 glacier-pools occur in various situations, and their geological effects 

 have been well pointed out by Charpentier *. 



A large glacier must have issued from Glen Nevis, and, owing to 

 the great height of the hills there, must, I should think, have pro- 

 truded across the mouth of the great valley of the Caledonian Canal, 

 after the ice had shrunk out of the mouth of Glen Spean. This 

 would continue to dam the water to a certain height, and may afford 

 the explanation of those broad terraces in the lower part of Glen 

 Spean, some of which are very noticeable. They differ in character 

 from the Parallel Roads, and few of them exceed an altitude of 

 400 feet above the sea. There is a fine fragment of one about that 

 height at Brackletter, and also at Auchnaderry, near Bridge of Roy, 

 and several at lower levels. It is worthy of remark that these 

 terraced accumulations all cease on approaching the mouth of Glen 

 Nevis. They are also absent in Glen Gluoy, and in the lower part 

 of Glen Arkaig. If they are of marine origin, why do they vanish 

 at these places ? 



§ 3. Place of the Parallel Roads in the history of the Glacial Period. 



a. Relation to the period of chief submergence. — Believing the Parallel 



* Essai sur les Glaciers, pp. 64 & 257. See also]Agassiz, Etudes sur les Gla- 

 ciers, pp. 217-288. 



