Geological Origin of the Present Scenery of Scotland 1 9 



once covered this country, lend their help to wear down the surface, 

 especially in valleys and hollows where, as Professor Ramsay has 

 pointed out, the erosive action of glacier-ice tends to scoop out 

 cavities, which afterwards become the basins of lakes. And thus, 

 by a system of slow excavation, the outlines of the country are 

 gradually carved out. 



In this prolonged process of denudation, many incidental features 

 conspire to modify the final results. I have alluded to the in- 

 fluence of underground movements; but more universal, and 

 perhaps even more important than these, are the eftects of the 

 varying texture and geological arrangement of the rocks. It is to 

 this latter cause that we owe those local modifications in the 

 scenery of the country, which form, indeed, its distinctive fea- 

 tures. Each well-marked variety of rock has usually a peculiar 

 mode of yielding to the forces of denudation, and this peculiarity, 

 gives rise to a special variety of outline in the landscape. This is 

 one of the most tempting parts of the subject ; but I must merely 

 refer to it, and urge the reader who wishes a new pleasure added 

 to his autumn tour, to take a geological map with him, and mark 

 as he goes along, how the character of the scenery varies with the 

 changes in the nature of the rocks underneath. The regions of 

 granite, gneiss, sandstone, limestone, trap-rocks, will each be 

 found to present certain specialities of outUne ; and by watching 

 this relationship between the external form and the internal texture 

 and structure of the rocks, he will become more and more con- 

 vinced, that it is mainly denudation which has brought about the 

 present relief of the country. 



In arguing against the common belief that the inequalities of 

 surface are chiefly the result of irregular upheavals and depressions, 

 or of fractures and open rents, I have tried to shew that these 

 inequalities are of such a kind, that no mere subterranean move- 

 ment could account for them, that they have been produced in the 

 main by the removal of solid material, and that this removal, so 

 far as known, could only have been the work of those denuding 

 agents which are still engaged in the task. It does not affect the 

 argument, whether we hold that the different powers of renovation 

 and decay were more vigorous in former times, or have always 

 been the same, on the whole, as they are now. The idea that 

 underground commotions, even of the most catclysmal kind, 

 could have opened our valleys and glens, seems to me excluded 

 by the facts of denudation. But though we are shut up, I beUeve, 



