﻿1861.] 



MURCHISON AND GEIKIE HIGHLANDS. 



179 



towards the interior of Ross-shire, their lower beds, particularly on 

 both sides of Loch Maree, either consist of conglomerates made up 

 exclusively of the gneiss on which they rest, including much white 

 quartz and felspar, or they are very coarse grits, which pass upwards 

 into the fine siliceous chocolate-coloured sandstone. This junction 

 of the lowest beds of the Cambrian is well exposed on the N.E. side 

 of Loch Maree, on the sides of the Haasach Stream, and partictdarly 

 at the base of the lofty mountain Sleugach, which is essentially a 

 Cambrian rock. There the fundamental gneiss, in low headlands, 

 dips S.W. at 70°, and the overlying sandstone, at 10° to 12°, to the 

 E. by N. 



Again, on the opposite or western side of Loch Maree, where the red 

 and chocolate-coloured sandstone, covered by gorgeously rich thickets 

 of fern, heather, and grand old Scotch-firs, approaches the older gneiss 

 of Gaiiloeh on which it rests, the basement-strata become first coarse 

 and gritty, and then form here and there pebbly conglomerates. 



From the western shores of Loch Maree this Cambrian sandstone 

 rises into a noble, lofty group, some of the summits of which, being 

 capped by whitish Lower Silurian quartz-rock, have led the natives 

 to style these mountains "Ben Too leach," or " the Grey Heads." 

 Looking from the hills east of Loch Maree to these mountains on 

 the west, which range from Ben Eay by Boostag to Ben Alii gen, 

 on the south side of Loch Torridon, the spectator has within his 

 vision massive mountains, whose summits range from 3000 to 3500 

 feet above the sea. Now, all the strata of this mountain-group, 

 which cannot on the whole be estimated as having a less thickness 

 than 7000 or 8000 feet, and which rest in unconformable positions 

 on the Laurentian gneiss, are on numerous summits capped by un- 

 conformable strata of quartz-rock with subordinate limestone. In 

 fact, the Cambrian strata undulate in such slightly inclined positions 

 as seldom to exceed 12° or 15°, whilst the subjacent gneiss and the 

 overlying quartz-rock are frequently highly inclined. These Cam- 

 brian rocks, whether inclining gently to the W.N.W. or to the 

 E.S.E., constitute therefore a thick series of intermediate strata, 

 which are quite unconformable both to the rocks beneath and to 

 those above them. 



In striking contrast to these unconformities, we shall presently 

 point out that, along a frontier of many miles in length, the geolo- 

 gist has no sooner passed over the fundamental gneiss and the Cam- 

 brian sandstone, and marked the transgressive junction of these 

 rocks with each other and also with the overlying quartz -rock, than 

 he meets thenceforward, in all the great overlying crystalline masses, 

 with a perfect conformity of direction of all the strata to each other ; 

 and that (omitting a few spots where local dislocations have oc- 

 curred) there exists a perfect ascending order from the Lower Silurian 

 quartz-rocks and limestone into younger and higher masses of mica- 

 ceous, quartzose, and chloritic rocks (including occasionally a younger 

 gneiss), not merely in the North-western Highlands, but also in the 

 Southern Highlands, including the Isles of Islay and Jura, and the 

 counties of Inverness, Argyll, Perthshire, &c. 



