348 Mr Milne on the Parallel Boads of Lochaber, 



twice in the 24 hours, but also a good deal of lateral current alter- 

 nately in opposite directions. Hence the sea, whilst it will eat into 

 the land more rapidly than a lake^ will also spread out more com- 

 pletely the detritus washed down into it. In a lake, on the other 

 hand, 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 in their upper surfaces, and presenting steep escarpmertts 

 towards the lake. 



Now, applying these two principles of tidal action to the shelves 

 of Lochaber, we seek in vain for any actual indentation into the 

 sides of the hills. The shelves consist entirely of buttresses which 

 stand out from the sides of the mountains ; and these buttresses, so 

 far from sloping at an angle little less steep than that of the sides of 

 the mountains (which should be the case with the sea), form flats or 

 terraces which deviate in general very slightly from the horizontal. 

 7. If the shelves were formed by the action of the sea, they should 

 he most distinct at 'places where the hill sides had been most ex- 

 posed. 



Thus, on the north and north-west sides of Craig Dhu, and on the 

 west side of Bohuntine, where there must, on Mr Darwin's theory, 

 have been an open expanse of ocean, the shelves should have been 

 most distinct. But at these places, the three highest shelves are en- 

 tirely absent ; the fourth alone is visible, though, being the lowest, 

 it must have been less exposed. It is quite anomalous, on the 

 marine theory, that the shelves should not have been formed where 

 the force of waves and of tidal currents must have been greatest, 

 and that they should have been most distinctly formed in the higher 

 and more sheltered parts of Glen Roy. 



The hills at the mouth of Glen Roy seem rather to indicate that 

 the highest shelves had not been formed on them, — the very reverse 

 of what might have been anticipated if Mr Darwin's views are sound. 

 If they had been formed, they would not have been obliterated, as is 

 manifest from the perfect preservation of shelf 4 on Craig Dhu and 

 Bohuntine. 



8. Having stated these objections to the theory of Mr Darwin, 

 I proceed to consider his objections to the theory that the shelves 

 were formed by lakes. 



These objections resolve entirely into the difficulty of explaining 

 the disappearance of the barriers, which must have dammed back the 

 •water in the valleys. But it would be no good reason for rejecting 

 an explanation founded on the existence of barriers, even though we 

 could not very clearly account for the disappearance of them, pro- 

 vided that there is direct and conclusive evidence that such barriers 

 existed. Now, I conceive that there is such evidence furnished by 

 the considerations before referred to. 



Let us examine, however, the alleged difficulty of explaining, how 



