180 PROCEEDINGS OF THE GEOIOGICAL SOCIETY. [Jan. 11, 



lake has been caused by the glaciers of the Cairngorm mountains 

 barricading the valley near Aviemore ; for I found the fine sandy 

 beds terminate towards Rothiemurcus, while great quantities of 

 granite -boulders and well-marked moraines occur on the flanks of 

 the hills on the west side of the Spey to the north of Aviemore. The 

 mineral quality of the debris composing these moraines is such as 

 to lead one to believe that they are due to glaciers that proceeded 

 from the high moimtains on the opposite side of the valley, while 

 their position further accords with this notion. We may easily 

 suppose that many lakes and large pools would arise from causes of 

 this nature, and from the irregular masses of debris left by the 

 glaciers acting as dams here and there, so as to obstruct the drain- 

 age of the valleys. 



In Arctic countries the periodical thawing of the ice occasions 

 great floods in the rivers, which at such times rise to great heights, 

 and overflow their banks to an extent that we in this country can 

 scarcely believe ; and there seems every reason to think that towards 

 the close of the Glacial period a similar state of things prevailed 

 here. I am therefore (disposed to credit the rivers with a large 

 share in the formation of our valley-gravels, as I did in a former 

 paper some years ago*. Nevertheless I stiU maintain, as I did then, 

 that there are some of these gravel-beds which mere river-action will 

 not explain. Thus at the northern extremity of the valley of the 

 Caledonian Canal, near Inverness, there are masses of coarse water- 

 worn gravel, rudely piled together in heaps, 200 feet thick, and 

 which I traced up the flank of the hill near the Limatic Asylum to 

 a height of 400 feet. Some of the pebbles are so large that one 

 might with more propriety call them boulders, instances being seen 

 of a diameter of from 2 to 4 feet. The stones, however, are all 

 water-roUed, and show no glacial striae. The stratification of this 

 gravel is often very far from horizontal, great undulations appearing 

 without any good development of false bedding. There is no very 

 great difference in the nature of the stuff" from top to bottom, so far 

 as I saw ; there is no clay, nor even silt ; all is of washed gravel, with 

 here and there some seams of fine sand, and there seems to be a 

 complete absence of all fossils. 



Now this valley of the Caledonian Canal forms a great gash across 

 Scotland from sea to sea, and its summit-level at Loch Oich is only 

 about 90 feet high. How, then, can any river-action account for this 

 immense pile of gravel near Inverness, reaching, as it does, to so 

 much greater a height ? The materials composing it look as if they 

 had been derived from the rocks along the valley to the south-west ; 

 and if they have come from that direction, how did they get past 

 Loch Ness, which is of great depth, in some places 780 feet. I 

 remarked that the pebbles are of various kinds of metamorphic and 

 crystalline schists, red sandstone and conglomerate, granites and 

 porphyries. This accumulation of gravel extends for a mUe or two 

 south-west of Inverness, beyond which it is not remarkable. Its 

 greatest development is near Dun Ian, where there is a good exposure 

 * Quart. Joiirn. Geol. Soc. vol. xvi. p. 353. 



