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IV.—On the Structure and Relations of the Deposits contained between the Primary Rocks and the Oolitic Series in the North of Scotland.

1829; Geological Society of London; Volume: 3; Issue: 1 Linguagem: Inglês

10.1144/transgslb.3.1.125

2058-1041

Adam C. Sedgwick, Roderick Impey Murchison,

Geology and Paleoclimatology Research

ALTHOUGH no good geological map of Scotland has yet been published, enough is known of its general structure to enable us to state, that nearly all the interior portions of the Highlands are composed of primary rocks generally exhibiting a slaty texture; and that, on the north-eastern and northwestern coasts, as well as on the southern flank of the Grampian chain, these primary rocks are succeeded by enormous masses of red sandstone and conglomerate, which, in several places (already described by one of the authors of this paper), are surmounted by a system of beds referrible to the lias and oolitic series of England.Our object in this communication is to describe the lower portion of these secondary deposits, viz. the masses of red sandstone and conglomerate;-to consider the natural groups into which they may be separated,-and, as far as possible, to bring them (as we have already done in describing the carboniferous series of the Isle of Arran) into comparison with formations of the same age in the southern parts of our island.The accompanying outline map*, partly constructed from our own observations, and partly derived from the works of M c Culloch, M. Boue, and other writers on the geology of Scotland, will convey a general notion of the geographical distribution of the masses we are about to describe.A glance of the eye over the map might induce us to suspect that they all belonged to one epoch, and even a slight examination of them would confirm the conclusion; for the conglomerates on the south-east flank of the Grampians are perfectly identical with those at the base of the secondary deposits of the Murray Firth and Caithness : and these, as will be hereafter shown, are strictly analogous to the conglome-* See Plate X I I I .at University of Saskatchewan on December 31, 2016 http://trn.lyellcollection.org/Downloaded from the Primary Rocks and the Oolitic Series in the North of Scotland.127 one who may hereafter examine the country.These introductory remarks are, we hope, sufficient to explain the objects we have in view, and the manner in which we purpose to introduce them in the following communication.§ 2. Range of the Old Red Conglomerates through Caithness, and on the Shores of the Murray Firth, Sfc.#c.After doubling Cape Wrath from the west, and proceeding nearly three miles along the northern coasts of Scotland, we first meet with the old red conglomerates in Kerwick bay.They are distinctly stratified, and dip towards the north at an angle which is inconsiderable when compared with the high inclination of the primary rocks on which they rest.They stretch along the coast towards Loch Durness, forming a succession of lofty precipices, which, here and there, are worn down into grotesque forms and detached pinnacles by the encroachments of the sea.Towards the interior they are also considerably extended, rising into an elevated ridge called Scrisish Ben, from which they descend to the south-west, and pass under the deep morasses of the district.Prom Loch Durness to the Kyle of Tongue we found no secondary rocks upon the coast; but immediately to the north-east of Lord Reay's house rises a remarkable, pyramidal hill called Craig-na-Vreckan to the height of about twelve hundred feet, which is entirely composed of the old conglomerate dipping off the coast at a low angle, and, like the deposit last described, resting unconformably upon the micaceous slate rocks of the district.On one side, these conglomerates descend into the cliff; on the other, they are prolonged into the heart of the country, and form several distinct, round-topped hills on the east side of a chain connected with Ben Loyal.Again, on the hills which stretch along the coast from Tongue to Strathyhead, we find no traces of undisturbed secondary rock : but, on approaching Strathy-water, there are a few loose blocks of conglomerate scattered on the surface; and thence to Glen Halladale boulders of the same kind are found in great abundance.It will appear from the subsequent descriptions of the formations of Caithness, that beds of sandstone and bituminous fetid limestone are first seen on the coast to the east of Strathy-water, and that the old conglomerate, forming the base of the whole system, is also seen in the cliff of Port Skerry.Combining this fact with the appearance of the boulders before mentioned, there can be no doubt that the old conglomerate is continued into the interior.We did not trace the whole of this zone, and therefore cannot assert its unbroken continuity; but we believe that a region of low conical hills forming an irregular south-eastern boundary to the morasses of Caithness, is chiefly composed