Mr. Bryce on the Parallel Roads of Lochaher. 103 



detrital matter to account for the barriers at the mouths of the glens, 

 required by the theory. The force of this objection would be very much 

 diminished, if we could receive Mr. Chambers' account of the hill of 

 Oonchan, as correct. It appears to me, however, that he quite over-esti- 

 mates the amount of detritus in this hill. 



After giving a fuU aud accurate description of the other principal 

 detrital accumulations of the district, Mr. Chambers thus notices the bill 

 of Oonchan : — " By far the grandest delta of the district is that hill 

 which has been referred to under the name of Unichan as occupying so 

 much of the lower part of Glen Spean. This is a mass of gravel 11 miles 

 long by perhaps 2 broad, reaching an elevation of 612 feet. I observed 

 rock rising through it at one place ; but it is mainly, as has been said, a 

 hiU of gravel." He considers that, "when the sea stood somewhat above 

 622 feet (and there is evidence of its having paused long at 628 or 630) 

 the rivers descending from the Ben Nevis group of mountains delivered 

 their spoils into the estuary filling Glen Spean : on the withdrawal of the 

 sea this mass was left." 



The high ground in question, part only of which is called Oonchan, is 

 an undulating ridge parallel to the main chain, aud stretching from near 

 Fort- William to within 1 J miles of the bridge of Roy, a distance of about 

 12 miles. Such subordinate elevations are seen at the base of almost 

 every high chain, and mark the axes along which the upheaving forces 

 acted with decreasing intensity. This ridge is separated from the main 

 chain by a slightly depressed tract, having a very smooth outline, into 

 which five glens, descending from the Ben Nevis group, open at right 

 angles, the surface presenting no marked change of character at the 

 junction. The streams from these glens, as well as those which drain the 

 tract itself, being prevented by the high ground in front from following 

 direct courses to the valley of the Spean, are deflected to the east and 

 west, parallel to the high ground on either side. The watershed of the 

 tract being nearer the western than the eastern end, and the inclination 

 eastwards slight, there is an imperfect discharge of the waters, and con- 

 sequently extensive swamps have been formed, which sometimes become 



3 



a. Steep slope of the Ben 



Nevis group. 



b. The hollow, or swampy 



tract. - 



c. Swelling top of the ridge. X -p 



d. Sidiis of Oonchan. ^ "^ -^ 



e. Kivcr Spean. 

 / Sloijon ascending towards 



Mocl-dbu. 



