368 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 15, 



Clasha, Ben Uarn More, and Gelly Cairn, I kept a constant look-out 

 for granite boulders, and was much surprised to find none (not even 

 one) on any of these hills, nor, as far as I remember, in the glens 

 between them, of which I traversed Glen Cluny, Glen Ey, Glen 

 Conny, and Glen Kristy. On the large mass of the Glas Meal I 

 noticed many boulders that presented a reddish granitic aspect ; but 

 on breaking them up, found them to be of a felspathic porphyry 

 quite different from the coarse red granite of the Ben Muic Dhui 

 group. It was only towards the mouth of Glen Ey that I noticed 

 some of granite. Now this is very remarkable on the supposition 

 that the blocks have been transported by floating ice, but would be 

 quite intelligible on a glacier-theory ; for large boulders from these 

 mountains are numerous in the valley of the Dee, and in the glens 

 and hills on the north side of that valley to the eastward of the 

 granite-masses. It is possible then, and perhaps probable, that the 

 land-ice has played a considerable part in the conveyance of the 

 larger erratic blocks from many of our mountains, although I am far 

 from restricting their transport entirely to such means. 



That there had been an extensive development of glaciers and 

 land-ice previous to the marine drift is, I think, likely from various 

 considerations. The absence of all earlier tertiary deposits, and the 

 fact of the drift resting so generally on the polished and striated 

 surface of the old rocks, without the interposition of any other beds, 

 bespeaks something singular in the previous history of the surface. 



No trace of laeustrine mud, fluviatile gravel, or buried forests, 

 testifies the pre-existence of ordinary land-conditions ; and it is 

 almost inconceivable that any advance of the sea, whether gradual 

 or sudden, could have so utterly annihilated all trace of these, espe- 

 cially in the inland valleys, where the waters would have assumed 

 the character of quiet sea-lochs, such as now indent the west coast of 

 Scotland. But if we assume a long period of land-ice, with glaciers 

 grinding down along the valleys for ages, and sludgy sheets of ice, like 

 those of Greenland, overspreading the rest of the surface, the absence 

 of all such remains becomes more intelligible. And when we further 

 consider that the character of the Mollusca of the English Crag- 

 formations indicates clearly a progressive diminution of temperature 

 previous to the marine drift (as is so well brought out by the 

 abstract of Mr. Wood's labours drawn up by Sir Charles Lyell in 

 the Supplement to the last edition of his ' Elements of Geology '), we 

 have some warrant for concluding that such may have really been 

 the case. 



The unstratified boulder-earth that occurs beneath the marine beds 

 of the Clyde and other districts may therefore, under this view, be 

 glacier- debris or moraine-matter levelled by the advancing sea- waters 

 of the drift-period. The immense profusion of transported blocks 

 and striated pebbles in many localities is more favourable to the idea 

 of glacier-action than of floating ice (for in some localities almost every 

 pebble is striated), as is also the pell-mell and hodge-podge mixture 

 of the fragments in the earthy mass. I have likewise shown that 

 the polished rock-surface beneath the drift is in certain cases almost 



