104 



Mr. Brtce on the Parallel Roads of Lochaler. 



lakes. The annexed sketch, No. -3, will give an idea of the outline of the 

 surface. 



On the western pai-t of the ridge the rock is seen in many places ; and 

 about the middle I found it a little lower than the highest point, c, of the 

 ridge at that part ; and I think there can be little doubt that the thick- 

 ness of the detrital covering is in most places inconsiderable. At its 

 eastern termination detritus appears in more imposing quantity. Near 

 the bridge of Roy the end of the ridge is cut through by niuuerous 

 streams, or rather the channels of streams, for there is often no water ; 

 and the detritvLS stands out in numerous round or elliptic flat-topped 

 mounds with steep sides. Towards the base of Cruachaninish and Ben- 

 chilinaig these are smaller and rounder, resembling Danish raths ; while 

 further back the detritus only shows in terraces, formed by the streams 

 cutting into the talus at the base of the high mountains ; as in Nos. 4 and 5. 



4 



a a Ascent towards the Ben Nevis group, h Gravel terrace, c Stream, 

 d Abraded surface. 



Mr. Chambers regards the question of the origin of the Parallel Eoads 



as " involved in that of the superficial formations generally, which bear 

 the marks of former levels of the sea at various intervals up to 1200 feet ;" 

 the various markings in the three kingdoms, in France, &c., " all falling 

 into such conformity as to prove that the shift of level has been effected 

 from at least that height, with perfect equability throughout." He con- 

 siders this widely extended and strongly marked conformity " as more 

 favourable to the idea of a recession of the sea, as opposed to that of an 

 elevation of the land, since it is precisely what woidd result from the 

 former operation, while there is an obvious difficulty in supposing " that 

 so large a portion of the earth's crust could be repeatedly upheaved, and 

 yet the relative levels so preserved that " between Paris and Inverness 

 not a vertical foot of derangement could be detected." 



The explanation of the origin of the Parallel Roads is thus mixed up 

 with, indeed forms an essential part of, his general theory. And what- 

 ever difficulty geologists may feel in giving their assent to such generali- 

 zations as those just quoted, or however unwilling they may be, in the 



