TRANSACTIONS OF THE SECTIONS. 81 



On the Physical Structure of the Highlands in connexion with their Geological 

 History. By His Grace The Duke of Argyll, K.T., F.R.S., F.G.S* 



The questions dealt with by Geological Science have now become so vast and 

 various, that no one district of country can be expected to furnish illusti-ations of 

 more than a very few of them. 



The West of Scotland, in the capital of which we are now assembled, is not rich 

 in deposits which illustrate the passage of animal life from the types that have 

 become extinct to those which are of more modern origin and which still survive. 

 No bone-caverns of importance have been discovered, and, with one exception, 

 even our river-gravels and estuarine deposits have not been especially productive. 

 That exception is, indeed, a great one. It was in this valley of the Clyde that the 

 late Mr. Smith, of Jordan Hill, first discovered those indications of an Arctic climate 

 recently prevailing which have ever since constituted a large and important branch 

 of geological inquiry, and the full interpretation of which still presents some of the 

 most curious and difficult problems with which we have to deal. But our Palaeozoic 

 areas, except the Coal Measures, are to a large extent singularly unfossiliferous. 

 Neither the Scottish Oolite nor Lias has yielded any remarkable additions to the 

 curious fauna of which in England and elsewhere they have yielded abundant 

 specimens. 



But, on the other hand, perhaps no area of country of equal extent in any quarter 

 of the world presents more remarkable phenomena than the West of Scotland, in 

 connexion with those causes of geological change which have determined the 

 form of the earth's surface, and have given to its physical geography those features 

 of variety and beauty which are the increasing delight of civilized and instructed 

 men. We cannot descend the com'se of this river Clyde to the noble estuary in 

 which it ends without having presented to us mountain outlines and an intiicate 

 distribution of sea and land which raise questions of the highest interest and of 

 the greatest difficulty. From the northern shores of that estuary to Cape Wrath, 

 in Sutherland, the country is occupied mainly by rocks of Silurian age, but so 

 highly crystalline as to be almost wholly destitute of fossils, and so upheaved, 

 twisted, contorted, and folded into a thousand different positions, that, except in 

 one great section, it is most difficult to trace any persistent succession of beds. It 

 is one great series of billowy undulations traversed by glens and valleys, some of 

 which are high above tlie level of the sea, but many of which are now so deeply 

 submerged that through them the ocean is admitted far into the bosom of the 

 hills. These glens and valleys lie in many different directions ; but there are so many 

 with one prevalent direction as to give a general character to the map, a direction 

 from N.E. to S.W., or parallel to the prevalent strike of the Silurian rocks. The 

 shapes of the hills and mountains are not by any means wholly without relation to 

 geological structure — because in a thousand cases the sloping outlines will be found 

 to be determined by the inclination of the beds, and the precipitous or steeper out- 

 lines to be determined by the upturned or broken edges. In like manner there are 

 cases where a crumpled or knotted outline is the index of beds deeply folded and 

 contorted along anticlinal axes. But nevertheless there are also innumerable cases 

 wherp no such relation can be traced ; where the mountains seem to have been cut 

 out of some solid mass, all the rest of which has been removed by some agency 

 which left these grea,t fragments standing by themselves, and of which the con- 

 tours cut across the lines of structure at every variety of angle. Along the whole 

 western face of this country it is guarded from the open ocean by an archipelago 

 of islands, some of which are separated from the mamland by submerged valleys 

 no broader than those which separate one hill from another in the inland glens. 

 Many of these islands are wholly occupied by the debris and the outbursts of extinct 

 volcanoes. The mountains which are thus composed bear, in many cases, the 

 characteristic forms of lava-streams ; but many others are not readily distinguish- 

 able in outline from the mountains of wholly different material which are near 

 them. They reach the same general average level of height, here and there 

 rising into peaks very similar to others of a widely different age and of a widely 



* Printed in full by order of the Council. 

 1876. " 9 



