396 The Parallel lioads of Glen Boy. 



they are entirely obliterated ; for instance, when they crosB 

 bare rock, where loose matter would not rest, and when the 

 surface of the hill is gently inclined, because their slope there 

 coincides with that of the alluyial cover. Very often their 

 appearance is so faint, that a spectator may find himself 

 standing on one without being aware of its existence ; but at 

 other parts they swell out into pretty broad terraces ; and 

 what seemed obscure to a spectator in juxtaposition with it, 

 becomes more distinct when seen from 

 the opposite side of the valley, where the 

 eye takes in the line for a length of some 

 miles, and the obscure parts and the well 

 marked parts are seen in connexion. Each 

 of these shelves or terraces has been 

 found by levelling to be perfectly horizon- 

 tal, both lengthwise and on the opposite 

 sides of the valley. In the annexed figure, 

 '^let h h represent a portion of the surface 

 of the hill, consisting of rock, with a 

 layer of clay and gravel resting upon it, 

 as indicated by the uneven line. The 

 Parallel Roads consist of thicker portions of this alluvial cover, 

 projecting slightly like a shelf or terrace. 



The first or lowest terrace a, is 972 feet above the level of 

 the sea. The second, b, is 212 feet higher, or 1184 feet above 

 the sea. The third, c, is 182 feet higher than the second, or 

 1266 feet above the sea. 



The shelves slope inward to the centre of the valley, (to the 

 line C, B, A). 



In the adjoining valley of Glen Gloy, separated by an 

 isthmus of high ground half a mile broad, there is a terrace 

 twelve feet higher than c, or 1278 feet above the sea, but 

 none lower. There is a remnant of a similar terrace at Kil- 

 finnin, fom' miles northward, which is forty feet higher than 

 c, or 1306 feet above the sea. The three terraces of Glen 

 Roy follow the line of the valley down to its junction with 

 Glen Spean, passing into all its sinuosities and recesses. 

 Here two of them disappear ; but the lowest continues its 



