4th Ridge. The great central range of the ancient commonty called Milbuy which overlooks all the other ridges, its elevation being 500 feet above the sea, and whose sides, sloping up to it as the great back-bone of the district, are shortest and steepest toward the north, but broader and more gentle in their southern inclination. Behind Belmaduthy House, this ridge attains its greatest altitude, but it thence proceeds with no interruptions or breaks in its outline, and generally of a pretty equal height, both towards Cromarty on the east and by Tore, Kilcoy Castle, and Ryefield on the west, to the valley which is watered by the rivers Orrin and Conon, which separate it from the sloping fields and rocky frontlets of Brahan. On the north, the Milbuy range subsides by several parallel but lower sandstone ridges, into the Dingwall or Cromarty Firth, and on the south it is separated from the third ridge above described, by the moss of Auchterflow, the cultivated grounds below Belmaduthy, and the flat or boggy land which separates the property of Tore from that of Redcastle.

The structure of the third and fourth ridges may now be considered together, and although between them and the first and second ridges above-mentioned, we have discovered no beds of the true mountain limestone of the coal measures, nor yet of the bituminous shales of Ferrindonald and Strathpeffer * which seem to represent them, yet we have little hesitation in assigning the geological place of these two ridges to the new red or variegated sandstone formation. Mr Miller’s recent fossil discoveries at Cromarty may, however, perhaps determine these ridges to be the upper beds of the old red sandstone deposit. Their strata are softer and finer in texture than those of the old red sandstone ridges. They have much fewer imbedded masses of conglomerate; they are more argillaceous, and abound in steatite and chlorite or green earth. No organic remains have as yet been seen in these strata, but in very many places they present the striped or variegated aspect whence the formation has acquired its name; some of the quarries, as on the estate of Rosehaugh and Suddy, exhibiting layers of alternate yellow, brown, and red colours, disposed in parallel streaks or ribbons. Several of the superior beds are also entirely yellow, or of a dusky white colour, whence it is suspected that they might perhaps be the outgoings in this direction of some of the colitic deposits, which at one time seem to have been extensively spread around the shores of the adjoining firth. The unusual fertility and deepness of soil, however, on these ridges prevent the rocks from being frequently seen, and the prolific nature of the materials into which they are decomposed, hence affords a farther indication of their belonging to the new red sandstone series, which abounds more largely with unctuous and clayish substances than such as occur in the older sandstone deposit.

As already stated, the sandstone ridges now enumerated have been affected at their eastern termination by a great granitic eruption or ridge which first appears in the cliffs of the Craigwood between Avoch and Fortrose, behind which it is covered with sand and gravel-banks, but the granite reappears on the north side of the burn of Rosemarkie, and thence composes several of the hills and cliffs along the coast, till, at the Sutors of Cromarty, it is found completely disencumbered of the secondary deposits. The rock, especially at its western boundary, consists chiefly of a hard, small granular and flesh-coloured granite, through which are interspersed in minute grains and coatings, crystals of black iron ore and lead glance. Numerous and large masses of gneiss also occur intermixed with beds of hornblende, actynolite slate and quartz rock, among which garnets are extensively disseminated, while the whole are everywhere charged with granite veins. The intrusion of such granitic invasion among the sandstone strata could not fail to have greatly affected them, and accordingly, on the estates of Avoch and Rosehaugh, the ridge of which seems to have been over a centre of volcanic action, we find the soft new red sandstone upheaved into short perpendicular hardened masses, the alteration and dislocation of the previously horizontal strata being seen to extend from the base to the very summit and crest of the ridge. On the opposite sides of the hill, the strata are seen thrown off in opposite directions, and even in the plains of Suddy the layers of the red sandstone are so irregularly disposed, and so often broken and disturbed, that it would be as useless as tedious to attempt to lay down with any degree of precision, the bearings or dip of the rocks. This confusion is worthy of notice, only as demonstrative of the greatness and extent of the granitic influence. That rock itself, with its various beds, falls to be more minutely described in the reports of the parishes of Rosemarkie and Cromarty. It is proper to add, however, that the great elevation of the Milbuy sandstones has been most probably occasioned by the same subterranean action, although we have not as yet seen the granitic rock cropping out on the surface, and in this view, it is likely that the basin of the Cromarty Frith was formed on the upheaving of the sandstone ridges along its sides, and that, before the invasion of the sea from between the Sutors, it consisted of a series of inland lakes or hollows.