In the Western Islands a minute portion occurs in Lewis; but elsewhere it is known only in Sky, where the quantity also is not considerable. That of Arran and Bute is indeed conspicuous; but these islands, as well as the great Cumbray, belong in this case, geo logically, to the adjoining mainland.
Resuming the sandstone of Orkney as a leading point, we find the same rock occupying the northern chore of Caithness,aud extending down the east coast towards the Ord, where it ceases for a time, while it also extends a considerable way into the interior coun try. Near Thurso it affords excellent slates of large dimensions, with flag stones, from the shales which are interstratified with it.
Every where, we need scarcely remark, it affords, or might afford, excellent building stone.
Resuming this rock again from the ord of Caith ness, we find it renewed beyond the Fleet, occupying a very wide tract on this shore, including Cromarty, and sketching down as far as the Moray Frith and Beauley. 'We must, however, observe here, that this portion is less continuous and less definable than that of Caithness, as masses of gneiss, often of great extent, intrude into it in many places, and as it also ramifies into some of the remoter Highland valleys, as towards St•athpeffer. On no part in this side of Ross and Sutherland does it rise into high moun tains.
On the western shore its aspect is far different, while its intricacy is such as to be indescribable ; being dispersed about among the gneiss and quartz rock of that shore, so that while in some places it extends for many miles without interruption, in others it occupies patches of only a few hundred yards in extent. Here also it rises into lofty moun tains, Kea-clod), formerly described as one of the loftiest of the Scottish hills, being formed entirely of this rock from the sea to the summit. Its general mineral character is here also different, as it is almost invariably red and of a much harder texture. More over, on the eastern shore, its outline is tame; hut here it not only produces some of the highest moun tains, but the characters of these are rugged, pre cipitous, and often peaked and serrated. We al
ready remarked the singular insulation of some of these hills, and as we must here add that the strata are generally at low angles, and often nearly hori zontal, it is evidently indicated that there has been a considerable waste or loss of rock, in consequence of what, in geological language, is called denuda tion.
Though we do not pretend to define this intricate boundary, we must say that it'forms a kind of belt along the western shore, sometimes skirting the sea coast and sometimes retiring inland, which extends nearly from Cape Wrath to Glenelg. Where broad est, this belt is about thirty miles wide, and where narrower, it sometimes does not reach to a mile; while, in some parts, it is altogether wanting. It also forms the chief of the Summer Islands. In this connexion it almost invariably succeeds to gneiss, but sometimes to quartz rock ; and in both these modes it sometimes forms mere summits, or caps on lofty mountains. Coul-beg is a very singular form of this kind, as is Suil-Veinn. We must also ob serve that it passes Cape Wrath so as to appear on the northern shore. here, and on the west coast, it produces some insulated stacks, or steeples, of great elevation, as well as of elegant forms, of which Stackacloa is peculiarly remarkable from its twinned shape.
\Ve must now return to Inverness, where we find this sandstone again as a continuation of that of Cro marty, occupying the country about Inverness itself, and reaching eastward beyond Speymouth, where this particular tract terminates. To the south, it sketches along Lochness, and chiefly on the eastern side, where it again terminates; while on the other shore a very scanty portipn only is found. It is here well known for the very great tract of conglomerate or pudding stone which belongs to it, and which is a subject of remark to all travellers.
Following this portion of sandstone still eastward, we find one narrower region of it occupying a small portion of Aberdeenshire; and with this may be said to end all the .sandstone of this character that belongs to the Highland district.