60 Mr Thomson on the Parallel Roads of Lochaber. 



is found to characterise the terraces. Now, there is probably 

 no doubt that important changes in the elevation of the land 

 have occurred since the commencement of the glacial period, 

 but I do not think that any proof can be given of their oc- 

 currence since its termination. In other words, I think no 

 proof can be adduced, that, ever since the last great disturb- 

 ance of the land, the climate has been so warm as to pre- 

 clude the supposition of the existence of glaciers round Ben 

 Nevis. Could this, however, be proved, still it does not ap- 

 pear to me that it would invalidate the glacial theory of the 

 terraces. It is easy to conceive that the whole of Scotland 

 might participate in a general elevation or depression ; each 

 part remaining unaltered in regard to inclination to the hori- 

 zon ; and even were we to suppose the south of Scotland to have 

 risen 30 feet, while the north remained stationary, and the 

 intervening parts moved in proportion to their distances from 

 the north, the utmost deviation from horizontality which 

 would thus be produced in the terraces would not exceed a 

 foot of difference between the levels of the northern and 

 southern extremities of any one of them ; an amount which 

 would be quite imperceptible by any mode of measurement 

 which could be applied on surfaces so uneven. 



In conclusion, I may remark, that, in calling in the aid of 

 glaciers towards the explanation of the Parallel Roads, no 

 gratuitous or unsupported assumption is made. So many 

 various and independent proofs of the existence of a glacial 

 climate in these countries, during some of the most recent 

 geological periods, have been accumulated, especially within 

 the last few years, that we may now regard it as an esta- 

 blished fact, and use it like a stepping-stone to assist us in 

 farther investigations. In addition to other proofs of a cold 

 climate derived ft*om organic remains, and from effects which 

 appear to have been produced by icebergs floating at sea, 

 indications of glaciers, in some instances of the most unequi- 

 vocal character, are to be met with in various mountainous 

 parts of Great Britain and Ireland. Such appearances, more 

 or less satisfactory, have been pointed out by various authors, 

 of whom it may be sufficient to mention Buckland, Lyell, 

 Bowman, Agassiz, Maclaren, and Forbes. In the island of 



