Prof. Nicol on Red Sandstones of the North-west of Scotland. 77 



the district, by Loch Assynt, the Kyles of Durness, and Loch 

 Eriboll, on the north, and on the south by Lochs Greinord, Gairloch, 

 Maree, Keeshorn, and Carron, and by a section of the southern part 

 of Skye. These sections present more or less uniformly the follow- 

 ing ascending series of rocks, which, excepting the lower gneiss, 

 have in general an inclination towards the S.E. : — 1. Gneiss, with 

 some granitic veins, and having a general N.W. and S.E. direction. 



2. Red conglomerates, grits, and sandstone, lying unconformably 

 on the gneiss, and exposed along a tract of about 20 miles in width : 

 these beds are at least 3000 feet thick, but rapidly thin off eastward. 



3. White quartzite, unconformable to the red sandstone, and fre- 

 quently accompanied by an overlying, hard, dark-coloured, siliceous 

 limestone ; these form a band about 10 miles wide, and are in places 

 at least 500 ft. thick. 4. Gneiss, occasionally of a different character 

 from the lower gneiss, and distinctly seen at many localities to over- 

 lie the quartzite. Gneiss also constitutes the country to the eastward. 



These rocks, with occasional serpentines, porphyries, and other 

 igneous rocks, were described in detail ; and it was stated that the 

 red sandstones (No. 2) were apparently unfossiliferous ; that the 

 quartzite presented some obscure evidences of organic remains ; and 

 that the limestone at Durness had furnished some univalve shells, 

 such as Euomphalus and Orthoceratites , besides other indistinct 

 fossils, first observed by Mr. Peach. 



1 he author pointed out that the red sandstones and conglomerates 

 (No. 2), occurring along the district described, decidedly form parts 

 of one series, and that, in his opinion, they are referable to the 

 Devonian age, whilst the overlying and unconformable quartzite and 

 limestone (No. 3), judging from their position and mineral character, 

 represent the Lower Carboniferous series of the South of Scotland ; 

 although in this he necessarily differs from Sir R. \. Murchison's opi- 

 nion, that the beds in question represent a part of the Silurian series. 



Prof. J. Nicol alluded to the difficulty of accounting for the super- 

 incumbent position of the gneiss, No. 4, which overlies the above- 

 described sedimentary rocks on the west, whilst a similar rock 

 underlies the true Old Red formation on the east, in Caithness. 

 Assuming, however, the continuity of the great mass of gneiss, he 

 points to certain igneous rocks, and other local evidences of disturb- 

 ance along the eastern limit of the quartzite, which may have resulted 

 in the forcing up of a portion of the lower gneiss over the sedimen- 

 tary beds ; whereas, on the other hand, the great degree of alteration 

 visible in the upper limestone and quartzite rather indicates, in his 

 opinion, that a metamorphosis in situ has affected the uj^permost beds 

 of the series. 



Tlie autlior concluded with a sketch of the physical changes which 

 this district must have successively undergone, from the deposition 

 of the conglomerates to the period of the elevation of these High- 

 lands into tlie region of ice and snow, and of the formation of 

 enormous glaciers among their ravines, traces of which still remain 

 in the " perched blocks " and local accumulations of drift, and in the 

 highly-polished surfaces of their hardest rocks. This period was 

 followed by subsidence, and by a still later partial elevation. 



