﻿178 



PROCEEDINGS OF TBCE GEOLOGICAL SOCIETY. 



[Feb. 6, 



tract, might be led to believe tbat this lower gneiss, being parallel 

 to the gneiss on the S.E., was truly part and parcel of the same 

 series of deposits as the rocks on the S.E. ; for in that case they 

 woidd only have to imagine the intervention of a stupendous fault. 

 But the plain fact entirely overthrows this hypothesis. The older 

 or gneissose limestone trends rectangularly to the direction which has 

 been assigned to it, and hence it cannot (being a true bed) traverse 

 the loch as represented. In fact, there is no trace of limestone on 

 the left or S.W. bank of Loch Maree, though, at some miles distant, 

 in Gairloch, and, again, subordinate to the north-westerly strike of 

 the Laurentian gneiss, another thin course of limestone has been 

 detected, and partially worked. In short, between Loch Maree and 

 the sea-board at Gairloch, wherever the fundamental gneiss is un- 

 covered in low masses beneath the superjacent masses of Cambrian 

 sandstone (the highly-inchned strata being admirably exposed in 

 the gorge wherein the River Kerry forms the picturesque Falls of 

 Andrcsy), the persistence of the N."W. strike is clearly maintained. 



Again, near Shieldag, and at the headlands on either side of the 

 mouth of the maritime Loch Torridon, as seen at the Point of Grabeg, 

 and extending up the loch westwards, the Laurentian gneiss has the 

 same north-westerly strike as in Loch Maree and Gairloch, in Suther- 

 land, and in the Lewis, and is seen dipping sharply to the N.E. 

 wherever its eroded edges thin off into low hummocks under the stu- 

 pendous and mountainous masses of the Cambrian sandstone forming 

 the ragged overhanging cliffs on both shores of Loch Torridon. 



In this district the underlying massive gneiss is perforated by 

 numberless intrusions of granite, as in the fiords of Sutherland, and 

 is in itself undistinguishable from the rocks of the same age which 

 range from Cape Wrath to Loch Liver*. It is therefore, we repeat, 

 most easily distinguished by its general aspect and structure from 

 the overlying flag-like rocks with which it has been confounded. 



II. Cahbriax Saxdstoxe axd Coxglojierate. 



In former memoirs these rocks, particularly as they occur in 

 Sutherland, have been so fully described, whether, as formerly, 

 under the misnomer of Old Red Sandstone, subsequently by Pro- 

 fessor Xicol as simply Red Sandstone, or by one of us as Cambrian, 

 that on this occasion we need only advert to them in their prolon- 

 gation through Ross-sliire from the north of Loch Broom on the 

 N.N.E. to Applecross on the S.S.W. 



In this tract these rocks range from about sixty miles in length, 

 and over an average width of not less than twenty miles, and form 

 clusters of mountains varying from 1500 to 3500 feet above the sea, 

 their lowest beds being seen in numeroiLS places to repose on the 

 Laurentian or fundamental gneiss. The promontories on both sides 

 of the marine Bay of Gairloch, as well as the noble mountains of 

 Applecross, consist of slightly inclined masses of this chocolate- 

 coloured sandstone, which there dip very gently seawards from off 

 the older gneiss, or to the "W.N.W. In following these same rocks 

 * Quart. Journ. Geol. Soc. vol. xv. p. 361 ; and vol. xvi. p. 218. 



