82S EEPORT — 1870. 



different material. Moreover all the islands partake largely of the general character 

 of the m.ainland in having their deeper valleys submerged, and in being thu^ 

 deepl}' indented by arms of the sea similar to those ■which give their peculiar out- 

 line to the adjacent coasts. 



It may serve to bring more vividly before j'ou the facts of the physical geogTaphy 

 of this country (for which it is one of the duties of geologists to account if they 

 can) if I give you some statistical facts affecting the single county of Argyll, 

 ■which beg-ins on the northern shore of the Firth of Clyde. Follo^wing the coast- 

 line of that county from the head of Loch Long, ■which is its southern and 

 eastern boundary, to Loch Aylort, ■which is its northern and western boundary, and 

 including its islands, we find it measures no less than 2289 miles in length, of 

 which aoout 840 represent the sinuosities of the mainland, and 1449 represent 

 the coast-line of its larger islands. There are, besides, valleys which are now 

 inland, and are occupied by freshwater lakes which evidently, at a recent period, 

 were arms of the sea ; and these represent a further line of coast, measuring 27G 

 miles. There are 11 principal arms of the sea, each of them measuring from one 

 to six and thirty miles in length. Two of the.se arms of the sea exceed the 100- 

 fathom line in depth — Jjoch Fyno and the Linnhe Loch ; and it is very remarkable 

 tliat these deep soundings do not occur near the points where these lochs join the 

 more open sea, but, on Ihe contrary, far up their course orbed among the mountains. 

 The ridges dividing these and other vallej's vary in elevation from hills of Acry 

 moderate height to the range of Cruachan, which immcdiatelj' beyond the boundary 

 of the county culminates in Ben Nevis, which rears its head almost on a level 

 ■with Ben MaclJliui, now ascertained to be the highest summit in the British 

 Isles. But no statistics can give an idea of the intricacj' with which sea and land 

 are interfolded on our western coasts comparable with that which is gained by some 

 of the many beautiful vievrs which abound on the heights in the vicinitj- of Oban, 

 whence the visitor can command the entrance of Loch Etive, with the course for 

 many miles of the Linnhe Loch, of the Sound of Mull, the Sound of Kerrera, and 

 the Firth of Lome. 



Now the question naturally arises — to what geological ages and to what 

 geological causes do we owe, in its main features, this curious distribution of land 

 and sea ? I say in its main features, because, of course, the more superficial 

 sculpturing of every moimtainous country is undergoing incessant modification; 

 and this modification may have been, and probably has been, very considerable 

 indeed within times which, geologically speaking, belong to the existing age. But 

 the question I put has reference to the epoch of past time, when the main outlines 

 of hill and valley were determined ; when the great mass of the country (which has 

 been, I believe correct]}-, identified as composed of metamorphosed Silurian beds) 

 was elevated into the various moimtain- chains which now constitute its charac- 

 teristic features. 



If the question had been asked some five and twenty years ago, I should have 

 said that the evidence pointed to an age of great geological antiquity for the 

 central group of Highland mountains, in some shape very like that in which we 

 see them. All round the edges of the country tliere are the remains of the Old Red 

 Sandstone, which often fit into the contour of the valleys and have left fragments 

 in nooks and recesses of the hills. It would almost seem as if thej' had been the 

 •shores of the seas or great lakes in which that great system of deposits was laid 

 down, and that they lifted their heads above those waters in forms not whoUj'' 

 unlike those in which we now see them. The total absence over almost the whole 

 country of any other or later rocks, the absence among the debris of any material 

 other than that of which the hills are themselves composed, would seem to confirm 

 tlie same general conclusion. 



Some doubt, however, may seem to have been thrown on this conclusion, since 

 it has become certain that it cannot be true of at least one district of our western 

 moimtains, which is ne-\'ertheless closely related to all the rest, having the same 

 general elevation, partaking of the same general bend of coast-lines, cut up by 

 .similar valleys, and fitting into the same contom-s of denudation. The district to 

 which I refer is that of the volcanic islands which stretch from the south end of 

 Mull to the north end of Skye. Since the discovery, which I v>-as fortunate enough 



