Mr Milne on the Parallel Uoads of Lochaber, 345 



larig, Glen Gluoy, and Glen Roy, whilst the Glen Gluoy stream 

 discharged only the waters of one lake. Mr Darwin did not visit 

 the Pass of Mukkul. If he had studied the appearances presented 

 by it, and by those almost as strikingly exhibited at Glen Glaster, 

 he would have found it impossible to deny that the waters which 

 formed shelves 3 and 4 flowed down river-courses, and therefore 

 could not be arms of the sea. 



His proposition is, *' that the waters of the sea, in the form of 

 narrow arms or lochs, such as those now deeply penetrating the 

 western coast, once entered and gradually retired from these several 

 valleys;" and he adds, that after considering the ** several and 

 successive steps of the argument, the theory of the marine origin of 

 the parallel roads of Lochaber, appears to me demonstrated T 

 (P. 56.) I regret that Mr Darwin should have expressed himself 

 in these very decided and confident terms, especially as his survey 

 was incomplete ; for I venture to think, that it can be satisfactorily 

 established that the parallel roads of Lochaber were formed by fresh 

 water lakes. 



1. The first circumstance which I shall notice as fatal to Mr 

 Darwin's theory, is suggested by the fact last referred to, that the 

 waters which formed the different shelves must have flowed out of 

 the gleiis^ and descended by river-courses to lower levels. The 

 waters which formed No. 1 shelf in Glen Gluoy descended nearly 

 29 feet by flowing into Glen Roy. The waters which formed No. 

 2 shelf in Glen Roy flowed in like manner into the valley of the 

 Spey. The waters which formed No. 3 shelf were discharged over 

 the head of Glen Glaster, down a slope of about 212 feet in vertical 

 height, into Glen Spean. Lastly, the waters which formed shelf 4 

 in Glen Spean, issued out of Loch Laggan by the ancient river- 

 course at Mukkul. 



Now, any one of these cases is irreconcilable with the notion that 

 the shelves had been formed by arms of the sea. There is no such 

 thing in nature as a river flowing out of an arm of the sea, to a 

 lower level. 



Mr Darwin, as we have seen, admits that this coincidence of the 

 shelves with water.-sheds, must be in some way connected with their 

 origin ; and, accordingly, he endeavours to give an explanation of it 

 consistently with this theory. He says that these water-sheds are 

 laiid straits^ with sea on each side of them, and that they consist 

 of littoral deposits or accumulations of matter formed by the oppo- 

 sition of tides. This opinion, however, is altogether inconsistent 

 with the actual circumstances of the case. In the first place, there 

 is at these water-sheds no accumulation of littoral deposits or de- 

 trital matter. They consist, generally, of bared rocks, forming 

 sloping channels or water-courses. In the second place, there is 

 no trace of water at the same level, on each side of these water-sheds. 

 In the third place, wh^ui land straits are formed by the accumu- 



VOL. XLIII. NO. LXXXVI. — OCTOBER 1847- Z 



