CHAP. XIII. PARALLEL EOADS OF GLEN ROT. 253 



same level on the opposite sides of the glen. Seen at a 

 distance, they appear like ledges, or roads, cut artificially out 

 of the sides of the hills ; but when we are upon them, we can 

 scarcely recognise their existence, so uneven is their surface, 

 and so covered with boulders. They are from ten to sixty 

 feet broad, and merely differ from the side of the mountain 

 by being somewhat less steep. 



On closer inspection, we find that these terraces are stra 

 tified in the ordinary manner of alluvial or littoral deposits, 

 as may be seen at those points where ravines have been 

 excavated by torrents. The parallel shelves, therefore, have 

 not been caused by denudation, but by the deposition of 

 detritus, precisely similar to that which is dispersed in 

 smaller quantities over the declivities of the hills above. 

 These hills consist of clay-slate, mica schist, and granite, 

 which rocks have been worn away and laid bare at a few 

 points immediately above the parallel roads. The lowest 

 of these roads is about 850 feet above the level of the 

 sea, the next about 212 feet higher, and the third 82 feet 

 above the second. There is a fourth shelf, which occurs 

 only in a contiguous valley called Grlen Grluoy, which is 

 twelve feet above the highest of all the Glen Eoy roads, and 

 consequently about 1,156 feet above the level of the sea.* One 

 only, the lowest of the three roads of Grlen Eoy, is continued 

 throughout Grlen Spean, a large valley with which Grlen Eoy 

 unites. (See Plate II. and map, fig. 36.) As the shelves, having 

 no slope towards the sea like ordinary river terraces, are always 

 at the same absolute height, they become continually more 

 elevated above the river in proportion as we descend each 

 valley ; and they at length terminate very abruptly, without 

 any obvious cause, or any change either in the shape of the 

 ground or in the composition or hardness of the rocks. 



* Another detached shelf also occurs at Kilfinnan. (See Map, p. 254.) 



