172 Geological Observations made in Scotland, 



faces have been disclosed by recent road-making operations, 

 of which one is distinctly a natural parting of the stone, 

 or an internal surface caused by sliding ; but the other of 

 them, which is covered with furrows and scratches, agrees 

 precisely with our smoothed surfaces produced by the sliding 

 of glaciers. But where should we seek for any source from 

 which glaciers could have spread themselves to this locality, 

 their motion being due to tfce force of gravity 1 The Gram- 

 pians — the nearest mountains of any considerable height — 

 have, with reference to this place, an angular elevation of 

 only about half a degree ; while those glaciers, at present 

 known, which approach most nearly to horizontality,* have 

 a slope of about three degrees. From Solothurn, where 

 ancient erratics from Wallis are to be found, to the summit 

 of the Alps at the Great St Bernard, we obtain a slope 

 amounting to 1^°; and how small does the portion of the 

 Scottish Highlands appear, which, under altered climatic 

 relations, might have been capable of supplying glaciers, 

 when it is brought into comparison with the regions of the 

 Alps. Similar difficulties, it appears to me, militate against 

 the ingenious hypothesis of Agassiz, that, by means of a 

 glacier proceeding from Ben-Nevis, the water in Glen Roy, 

 to which the celebrated Parallel Roads are attributed as 

 beaches, has been confined. It is not the requisite fall, 

 however, but a sufficiently extensive plateau which, in this 

 case, is wanting. On account of such objections as have 

 just been stated, it is natural to expect that there should be, 

 as there actually are, in Great Britain and Scandinavia, 

 many and eminent adherents to the explanation of the dilu- 

 vial and erratic phenomena, by means of the rising of the 



* In Mr Thomson's paper on the Parallel Roads of Lochaber, published in 

 the Edinburgh New Philosophical Journal for July 1848, in paragraphs 13 

 and 14 of the paper he points out what appears to him to be quite a satisfac- 

 tory explanation of the fact, that the present Swiss glaciers do not spread much 

 over the low level land, and explains the peculiar state of the climate of Scot- 

 land, which he conceives would occasion the glacier, whose former existence in 

 in this country is indicated by such facts as those adduced in the letter of Pro- 

 fessor Studer. Mr Thomson thinks much misconception, regarding the possible 

 existence of glaciers, under various circumstances, has arisen from a too exclu- 

 sive study of those at present met with in Switzerland. 



