18411880] GLEN ROY 183 



however, yet believe in the glacier theory, for reasons which Letter 522 

 I will presently give. 



There are three chief hostile considerations in Mr. Milne's 

 paper. First, the Glen [shelf?], not coinciding in height with 

 the upper one [outlet?], from observations giving 12 ft., 15 ft., 

 29 ft, 23 ft. : if the latter are correct the terrace must be quite 

 independent, and the case is hostile ; but Mr. Milne shows that 

 there is one in Glen Roy 14 ft. below the upper one, and a 

 second one again (which I observed) beneath this, and then 

 we come to the proper second shelf. Hence there is no great 

 improbability in an independent shelf having been found in 

 Glen Gluoy. 



This leads me to Mr. Milne's second class of facts (obvious 

 to every one), namely the non-extension of the three shelves 

 beyond Glen Roy ; but I abide by what I have written on 

 that point, and repeat that if in Glen Roy, where circumstances 

 have been so favourable for the preservation or formation of 

 the terraces, a terrace could be formed quite plain for three- 

 quarters of a mile with hardly a trace elsewhere, we cannot 

 argue, from the non-existence of shelves, that water did not 

 stand at the same levels in other valleys. Feeling absolutely 

 convinced that there was no barrier of detritus at the mouth 

 of Glen Roy, and pretty well convinced that there was none 

 of ice, the manner in which the terraces die out when entering 

 Glen Spean, which must have been a tideway, shows on what 

 small circumstances the formation of these shelves depended. 

 With respect to the non-existence of shelves in other parts of 

 Scotland, Mr. Milne shows that many others do exist, and 

 their heights above the sea have not yet been carefully 

 measured, nor have even those of Glen Roy, which I suspect 

 are all 100 feet too high. Moreover, according to Bravais, 1 

 we must not feel sure that either the absolute height or the 

 intermediate heights between the terraces would be at all the 

 same at distant points. In levelling the terraces in Lochaber, 

 all, I believe, have been taken in Glen Roy, nearly N. and S. 

 There should be levels taken at right angles to this line and 

 to the Great Glen of Scotland or chief line of elevation. 



Thirdly, the nature of the outlets from the supposed lakes. 



1 " On the Lines of Ancient Level of the Sea in Finmark." By A. 

 Bravais, Member of the Scientific Commission of the North. Quart. 

 Jonrn. Geol. Soc., Vol. I., p. 534, 1845 (a translation). 



