ON THE NATURAL HISTORY OF THE SOUTH OF SCOTLAND. 237 



clients. The layers are usually thin, varying from a foDt or more to a 

 few inches. 



. Less aggregated, or moi-e decomposed and earthy, the rock assumes a dull-red 

 colour, presenting the appearance of a sandstone, but very readily distinguishable 

 by its other characters. The fissures often present a ferruginous clayey matter, 

 and the rock is less tenacious. 



Next, it becomes very fine-grained, with numberless glistening points, and 

 very readily splits into plates an inch or less in- thickness, the interior of which is 

 not laminar, but yields an uneven or conchoidal fracture in whatever direction it 

 is broken. This is the common grey-wacke slate. 



The laminae becoming smaller, and the texture finer, with a lamellar disposi- 

 tion, the grey-wacke slate passes into transition clay-slate, which is glistening 

 with minute points, but does not present the glossy surfaces of the primitive 

 clay-slates, which seem to form a passage from the micaceous and chloritic slates. 

 The grey-wacke clay-slates are always easily distinguishable from the primitive, 

 although their colours may be nearly the same. They are never so hard, their 

 laminae are less coherent, and they decompose more readily. 



Becoming still finer, and assuming a black or grey tint, without lustre, the 

 slates pass into shales resembling those of the secondary formation, from which 

 they often cannot be distinguished in cabinet specimens. Having the same 

 carbonaceous aspect, with shining surfaces, they become glossy alum-shale, as in 

 the ravines of Hartfell and White Coom. 



All these varieties, but especially the slates and shales, have a tendency to 

 break into rhomboidal fragments, of which the acute angle is about 65°. I have 

 remarked curious tortuous impressions between the laminae of the slate, but am 

 unable to say whether they are indicative of the remains of organic matter 

 or not. 



Quartz, calcareous spar, and heavy spar, chlorite, and iron-pyrites, are the 

 only minerals which I have seen in veins or nodules in these rocks. Galena, 

 however, has been found in a few places, as on Mannor Water, and it is reported 

 that a silver, some say a gold mine, was formerly worked in Megget-dale. 



In form the hills approximate in a considerable degree to many of the granitic 

 masses of Aberdeenshire, but they never present the precipices and corries which 

 characterize the more elevated of the latter. 



The whole district, with its rounded, smooth-sloped mountains, connected in 

 elongated heaps, its long, narrow, straight, or slightly tortuous vallies, its argil- 

 laceous and pebbly soil, its clear and rapid streams, and its grassy vegetation, 

 with the absence of natural wood, and the scarcity of artificial, forms a strong 

 contrast to the mountainous district of the middle and northern divisions of 

 Scotland, in which peaked, serrated and ridgy mountains with crags and corries, 



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