Chap. VIII.] 
LOWER SILURIAN, NORTHERNJHIGHLANDS. 
167 
hence it follows that the older gneiss cannot be supposed to be reproduced 
as a surface-rock in the lofty mountains of the Central Highlands with- 
out calling in faults and inversions of stupendous dimensions. "Wherever 
faults exist, it has been shown by Mr. Geikie and myself (Quart. Journ. 
Geol. Soc. vol. xvii. p. 193) that the order of superposition which I have 
indicated is always maintained. Again, if the Laurentian gneiss had been 
brought anew to the surface in the Central Highlands or on the east coast, 
we should expect to find it with the same characters and direction as in the 
west, and equally surmounted by Cambrian conglomerates and Lower Si- 
lurian quartz-rocks and limestones. But this is never the case ; and the 
truth is, that all the rocks we see on the west coast are deeply buried, as 
we advance to the east and south, under flag-like micaceous strata, which 
are very dissimilar to the old Laurentian gneiss. 
The granitic veins of the north-west coast are, indeed, essentially dif- 
ferent from the massive granites of the east. The former are subordinate 
to a rock which underlies the oldest conglomerate and sandstone of the 
British Isles, whilst those of the south-east penetrate and alter strata that 
are evidently nothing but mica-schists and quartzose flagstones, which, 
though essentially different from the old gneiss at certain distances from 
such granitic intrusions, have necessarily some resemblance to them at such 
points of alteration and contact. Yet, that these mica-schists and flaggy 
beds of the east really overlie all the inferior masses of older gneiss, Cam- 
brian sandstones, and Lower Silurian quartzites and limestones, no one can 
doubt who proceeds from Assynt, by Strath Oikel and Lairg, to Bonar 
Bridge. He will there see that all the Lower Silurian rocks of the north- 
west and west are covered by a flag-like micaceous series of very different 
and uniform structure, the strata of which dip steadily to the E.S.E., par- 
ticularly on the banks of the Oikel, until they are broken through by the 
younger granitic masses in question, and are at such points necessarily both 
altered and much dislocated. 
Again, if some one should suggest that the quartz-rock of the Scarabin 
Hills of the south-eastern part of Caithness may represent the old lower 
quartz-rocks of the west coast, I would beg him to examine the structure 
and relations of the two, and he will abandon that idea. The quartzites 
of the west are manifestly altered sandstones which, whether they lie 
upon purple Cambrian conglomerate and sandstone or on the ancient 
gneiss, are quite distinct from the pure quartz-rock of the Scarabins, 
which is simply a mass of the grey overlying quartzose rocks void of lime- 
stones, and metamorphosed by the powerful eruptions of granite which, 
enveloping all such stratified rocks on the banks of the Langwell and 
Berridale Rivers, jut out on the coast in the bold promontory of the Ord 
of Caithness, where the passage of the granite into compact felspar-rock 
may be admirably studied. 
However, therefore, certain details may hereafter be settled, this great 
