408 MR MILNE ON THE PARALLEL ROADS OF LOCHABER. 



boulder-clav in Scotland, the sea has stood at least 1000 feet higher on the land 

 than at present. Of course, it must have been after the land rose out of the sea 

 to some extent, that the Lochii1)er shelves could have been formed by lakes ; but 

 the lowest of these might have existed when the sea stood 800 feet above its pre- 

 sent level, in which case the depth of detrital matter required to dam up the 

 valleys would be comparatively small. 



1 have attempted to explain how the valleys of Glen Roy, Glen Gollarig, and 

 Glen Spean, were blocked up. There still remains Glen Gluoy, which, as before 

 mentioned, contains two shelves, one of which is about 29 feet above the highest 

 of Glen Roy. Glen Gluoy being unconnected with the other valleys, requires a 

 separate blockage. There would be no great difficulty in imagining the existence 

 of detrital blockage in this glen, at the place where its shelves terminate towards 

 the west, as it is generally, throughout its whole course, exceedingly narrow ; and 

 being unconnected with Glen Roy (though MacCulloch states the reverse), its 

 blockage may have been worn down at periods, and in a way, independently of 

 Glen Roy and Glen CoUarig. 



Before, however, forming a very decided opinion as to the position of the 

 blockage applicable to Glen Gluoy, I should like to examine more particularly 

 than 1 was able to do, some of the other Glens which open into the Caledonian 

 valley on both sides, with the view of ascertaining whether they contain traces of 

 •horizontal shelves about the same height. Mr Dahwin takes notice of one in 

 the valley of Kilfinnin,* about 10 miles to the eastward, and which he says is 

 (by his barometric observations) about 40 feet ab(jve the highest shelf in Glen 

 Roy ; in which case it would be only 10 or 11 feet above that in Glen Gluoy, a 

 difference quite within the limits of error. 



1 have observed several places along the Caledonial Canal, where there are 

 traces of one or more horizontal terraces, at a height of from 650 to 090 feet above 

 the sea. From these considerations, I infer the possibility of there having been a 

 blockage which applied not merely to Glen Gluoy, but to other glens opening into 

 the great Caledonian valley ; and it would, therefore, be most important, that 

 future observers should turn their attention to the adjoining districts. 



My explanation of the Lochaber shelves depends entirely on the accuracy of 

 the supposition, that the valleys were, in the lower parts of them, filled up with 

 detrital matter, capable of being gradually worn down and washed away. This 

 supposition is not only not improbable on general principles, but is verified to a 

 great extent by the remains of such detrital matter at and above the heights 

 required for it. Thus, in Glen CoUarig, there are to be seen, near the east end, 



* It is to 1)6 resetted that Mr Darwin, when he visited Lochaber, was not pro\nded with a 

 spirit-level. His statement as to the horizontality of this shelf at Kilfinnin, depends entirely on 

 ocular inspection and barometric measurements. 



