NICOL SOUTHEKN GEAMPIANS. 207 



am inclined to regard as, in this locality, a lower formation than the 

 mica-slate, and thus not connected with that in the central region. 



The whole of this western region, however, is so much disturbed 

 by igneous intrusive rocks, and the wild nature of the country, with 

 the uncertainty of the climate, renders continuous geological inves- 

 tigation so difficult, that few certain conclusions can be drawn from 

 the sections as to the relations of the stratified masses. Still, on the 

 whole, I adhere to the view stated by me in 1858, that the quartzite 

 and gneiss of the Black Mount and Breadalbane Highlands form a 

 wide synclinal trough resting on both sides on mica-slate, and thus is 

 an overlying and younger formation. On the other hand, the gneiss 

 near Ben Nevis, and probably also that towards Loch Treig, appears to 

 me an older formation. So also the great gneiss-formation on the 

 west side of the Great Glen. This singular depression is evidently 

 the line of a great fault, so that the connexion of the strata on its 

 two sides is very uncertain. On the upper Loch Eil beyond Corpach 

 the gneiss dips to the west, but this is clearly connected with the 

 granite which forms the hills along the west side of the Lochy. 



The mica-slate of Loch Creran, with some similar strata seen in 

 other parts of the western Highlands, is probably also a peculiar 

 formation, distinct both from the ordinary mica- slate and also from 

 the clay-slate. In regard to age, I conjecture — for with so few certain 

 facts little more is possible — that it is younger than the mica-slate, 

 and older than the clay-slate. 



The clay-slate, limestone, and quartzites of Appin and Balahulish 

 are, we have seen, unconformable to the mica-slate, and probably an 

 overlying formation. I still conjoin them with the slates of Easdale 

 and Islay, though the black carbonaceous beds so common at Easdale 

 and Oban are not seen at Balahulish, and the deposits also differ in 

 other respects. As in 1858, 1 am still inclined to regard these rocks 

 as the newest deposits in this region. I then stated that these 

 slates were the equivalents of the Lower Silurian (Skiddaw Slates)*, 

 and Sir lloderick I. Murchison has since expressed his concurrence 

 in this view. These slates and limestones thin out north of Loch 

 Leven, and do not seem to be represented near Ben Nevis or further 

 north. The partial beds of limestone quarried in Glen Spean belong 

 to the mica-slate, and thus to an older group. 



23. Geological connexion of the Grampians with other parts of the 

 Highlands. — Before concluding this paper, I may be allowed to say a 

 few words on the connexion of these beds with the strata in other 

 parts of Scotland. In such comparisons we are deprived of one 

 great means of identification of distant formations by the entire want 

 of organic remains. Except some obscure indications noticed by me 

 in a former communication, no traces of organic beings have ever 

 been mentioned from these beds. We are thus thrown entirely on 

 the mineral character of the rocks and their geological relations for 

 any conclusions we may form in reference to these points. There is no 

 doubt that ultimately all Geology of the primary rocks must depend on 

 these characters as the basis of its classifications ; but as there is reason 

 * Quart. Journ. Geol. Soc. vol. xv. (1858) pp. 112, 116. 



