140 Dr Murray on the Natural History of Afford. 



fer, beyond its present limits, as to enable us to solve the problem in ques- 

 tion ? 



It has been already hinted, that certain vegetables require a certain depth 

 of soil ; and, upon this principle, the degree of tendency to disintegration pos- 

 sessed by the rocks is connected with the vegetable products. Thus, on the 

 north side of the Alford district, where the rocks have a peculiarly micaceous 

 character, and readily crumble down, the mineral soil, and, consequently, the 

 vegetable, is deeper than on the other hills ; and there the heather is most 

 mixed with grass, and the native berries most abundant and perfect. It will 

 be readily admitted that exceptions exist to the opinion that soils are not in- 

 dicated by their natural products, and perhaps none is more remarkable than 

 may be adduced from the Green Hill of Strathdon. This has been already no- 

 ticed on account of its peculiar rock ; and, it is remarkable, that its vegetation 

 is also peculiar, entirely different from that of the contiguous hills. These 

 are invariably clothed with the heaths ; but the hill just mentioned derives its 

 name from a green covering of grass. It produces, as is also worthy of no- 

 tice, Arenaria vema, Cochlearia officinalis, and Statice armeria, of which the 

 two last are extremely rare in that quarter ; and as to Arenaria verna, I never 

 met with it in that part of Scotland, unless in the spot mentioned, and again 

 at Leslie, growing on the very serpentine rock with which it is associated at 

 Strathdon. I have thus admitted some striking exceptions to what I have 

 ventured to bring forward as the general result of observation ; but it may be 

 asked, Whether the exceptions are more numerous than those which present 

 themselves against every general rule ? If it were stated that the conclusion 

 here supported must be inaccurate, because the vegetation of the hill is always 

 different from that of the moor or the bog, I should answer, that this depends 

 not strictly upon the ingredients of the soil, but rather upon other circum- 

 stances, namely, its wetness and depth. Let a wet spot on a hill be examined, 

 and there will be found not the heaths, &c. which cover the thin dry soil in 

 the neighbourhood, but the same grass, the same rush, the same willow-herb, 

 &c. as in the plain below. The wetness favouring luxuriance, produces an in- 

 crease of that soil which is formed by the decay of vegetables ; and plants, 

 which could not find a place in the adjacent thin and dry stratum of peat, fix 

 themselves and thrive in this moister and deeper soil, though it be not che- 

 mically diflferent from that which surrounds it. No doubt, if we go to a cer- 

 tain height, the vegetation undergoes an alteration ; but this may depend upon 

 the cold and dryness, rather than on any change in the chemical ingredients. 

 But, after all, how few are the truly alpine plants of Europe, in comparison 

 with those which are occasionally found at almost every altitude ? 



Effects of Hoar-Frost on Plants. 



The thermometer at Alford has a greater range than at the seaside, the 

 temperature being higher during the hottest months, and lower during win- 

 ter, than in the neighbourhood of the sea. I, however, made at Alford no 

 observations on the thermometer extensive enough for being mentioned ; but 

 I may notice, that, in a late number of the Edinburgh Journal of Science, it is 

 stated, on the authority of Mr Fairholme, that, one morning in winter 1825-6, 



