1867.] LUBBOCK PARALLEL ROADS OF GLEN ROY. 87 



high an angle as that indicated by him, I doubt whether the still 

 waters of an inland lake would have sufficient power to eat them 

 away. Moreover the case is not one of mere erosion. 



Mr. Darwin expresses himself as follows : — 



The shelves *' seem to have been formed, as suggested by Mac- 

 culloch, by the check given to the downward descent of ordinary 

 detritus, and that transported by torrents, at the level of the ancient 

 waters " (p. 41). Again — 



" The fringe of rudely stratified alluvium, the origin of which we 

 are considering, resembles, both in structure and composition, such 

 beds of detritus as would have accumulated on the shores of a lake 

 had one existed in these valleys" (p. 51). And once more — 



*' The two regular shelves are, perhaps, more plainly marked here 

 than in any other part of the whole glen ; and it would appear pro- 

 bable that this is owing to that portion having been exposed to a 

 longer space of open water, by which means the ancient waves 

 acquired a greater than ordinary power in heaping up detritus " 

 (p. 62). 



Mr. Milne-Holme does not enter much into this part of the subject. 

 He says, however, " In a lake which has no movements'of water either 

 vertical or lateral, the detritus deposited on the sides of a valley 

 occupied by it will be scarcely if at all removed, and will thus form 

 projecting buttresses nearly flat on their upper surfaces, and present- 

 ing steep escarpments towards the lake"*. 



Prof. Rogers f regards the roads as *' nearly level, wide, deep 

 grooves in the easilji eroded boulder-drift or diluvium which, to a 

 greater or less thickness, everywhere clothes the sides of these 

 mountains ;" and he supposes these grooves to have been cut by a 

 great inundation coming from the Atlantic. 



Mr. Eobert Chambers J also considers the roads to be " lines of 

 indentation " in the otherwise uniform slope of the hill. 



Mr. Jamieson follows Macculloch. The terraces are formed, ac- 

 cording to him, " by the check which the water of the old lake gave 

 to the descent of the debris washed into it by the rains and streams, 

 as Macculloch long ago pointed out. They are, if I might nse the 

 expression, the continuous deltas formed by the rains and other 

 atmospheric agents " §. 



Finally, Sir C. Lyell expresses himself as follows : — " The parallel 

 shelves 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" ||. 



" It is well known that wherever a lake or marine fiord exists, 

 surrounded by steep mountains subject to disintegration by frost or 

 the action of torrents, some loose matter is washed down annually, 

 especially dming the melting of snow, and a check is given to the 

 descent of this detritus at the point where it reaches the waters of 



* Edinburgh Royal Soc. Trans, vol. xvi. 1847. 



t Lecture at the Royal Institution, March 22, 1861. 



X Ancient Sea Margins. § Quart. Journ. Geol. Soc. vol. xix, p. 238^ 



II Antiquity of Man, p. 253. 



