ON THE NATURAL HISTORY OF THE SOUTH OF SCOTLAND, 237 
dients. The layers are usually thin, varying from a foot or more to a 
few inches. 
Less aggregated, or more 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 laminse 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 
laminse 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. 
Alt 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 laminse 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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