I860.] JAMIES0N DRIFT, ABEltDEENSUlKE. 367 



but I observed here and there, as I went along, fragments of a 

 peculiar land of porphyry that I had met with in sihi on a lower 

 ridge to the northward. These fragments continued to occur, 

 although very sparingly, high up on the shoulder of the mountain ; 

 but on the very top I looked some time for them in vain. A prop 

 or cairn on the summit, apparently the work of the Ordnance 

 Surveyors, showed nought but quartz, the sharply angular debris of 

 which strewed the protruding edges of the strata, clothed here and 

 there with a carpet of fine soft moss, the last stunted patch of heather 

 having failed considerably lower down. A single Alpine Hare was 

 the only living creature I saw on this lone mountain. Searching 

 about amongst the quartz-debris I did, however, find, on the very top 

 of the hill, a small lump or two of the same porphyry ; and other frag- 

 ments of it occurred as I descended the shoulder of the mountain. 

 Although a dike of this porphyry may run through some part of the 

 bill, yet I think I may safely say it does not appear on the very crest ; 

 for, owing to the absence of vegetation on the sterile siliceous rock, 

 the strata are so bare that I could scarcely have missed seeing it : 

 and if any vein of it did occur, its fragments ought to be much more 

 numerous ; for, as I have mentioned, it was only after some scrutiny 

 that I could detect some two or three pieces. I question, indeed, 

 whether any such porphyry now exists at so high an elevation in this 

 part of Scotland. 



Perhaps the most probable supposition with regard to these and 

 other like cases is, that ridges of the absent rock may have originally 

 existed at greater heights, and that such fragments have been 

 scattered about during the denudation that has gone on in earlier 

 geological periods. Still, looking at the numerous instances of high- 

 lying boulders that have undoubtedly been transported during the 

 Pleistocene epoch, we cannot help speculating on the probability of 

 these also having been lodged where they now lie during the same 

 period. 



And in connexion with this I may here remark that I found no 

 foreign fragments on the tops of the granite mountains of the Ben 

 Muic Dhui group that attain elevations approaching 4000 feet and 

 upwards. Some of these I examined narrowly with this especial 

 view, particularly the extensive table-like summit of Ben-a-Buird, 

 where I thought, if anywhere, they might be found. But nothing 

 met the eye save granite blocks and granite sand, with occasional 

 pieces of white quart/, veins of which are common in these mountains, 



§ 5. One circumstance struck me as worthy of notice in reference to 

 the dispersion of blocks from these granite hills. They lie in a great 

 cluster on the north side of the River Dee; while to the south of its 

 valley rises a chain of quartz mountains of considerable magnitude, 

 intersected by numerous glens. On the theory, then, of a transport 

 duo to floating ice urged by a current from the north, it was to be 

 expected that many of these granite blocks would pass across the 

 valley on their ice-rafts, and be arrested on the higher pints of this 

 quart/, chain immediately opposite. A.ocordingrj . in I reversing Borne 

 of the principal members of the group, via. the Glas Meal, Cairn-na- 



