20 Notices of Memoirs. 



frosts and other agencies, tended to reduce to its own level the solid 

 lands, with all their infinite variety of outline. It was no less 

 generally known how the Geological structure of a country must 

 always influence its configuration — how the softer rocks would 

 generally lie in the valleys, and those of a more durable nature oc- 

 cupy the heights — how the contour of the heights would vary accord- 

 ing as these were formed of schists of granite, of dolerite, of quartz- 

 rock, or of any other well-marked species — and how this peculiar cha- 

 racter was due to the unequal manner in which the different masses 

 yielded to the touch of the atmospheric forces, so that a trained eye 

 could oftentimes detect at a considerable distance the nature of the 

 rocks by reference to the aspect of the hills alone. But while all 

 were willing to admit that the subaerial agents might do something 

 towards modifying the surface of a country, yet many would not 

 allow that its straths and valleys had been mainly formed by these 

 seemingly feeble forces. Nor when we reflected on the enormous 

 time required by the hypothesis which they rejected, could it be 

 wondered at that some geologists, whose chief stumbling-block was 

 time, should have summoned up subterranean action to account for 

 certain appearances connected with the superficial phenomena of our 

 country, still less should we be surprised when the sea was appealed 

 to as having been chiefly instrumental in moulding the land into hill 

 and dale. 



There were probably few who began this study, that were not at first 

 more deeply impressed with the energetic action of the waves along a 

 sea-coast, than with the less obtrusive work carried on by the subaerial 

 forces. Gaunt cliffs and long-retiring caves and inlets seemed to assure 

 them, that rather in the restless activity of the breakers, than in the 

 puny rains and rivers of the land, they had found the power which 

 hollowed out the deep places of the earth. No one could heartily 

 accept the theory which referred to atmospheric erosion the mould- 

 ing of the land into hill and valley, who had not worked out his 

 belief for himself in the field. This was the only way to learn 

 what denudation, whether submarine or subaerial, really was. 

 When we came impartially to consider the subject, we should find 

 that a vast variety of agents had been at work, from the earliest 

 geological times, in shaping out the contour of our country. Thus, 

 it was not disputed that subterranean movements of elevation and 

 depression, and the waves and currents of the sea, had, in many 

 cases, determined the direction in which streams and rivers should 

 flow ; but the cutting out of the valleys and the fashioning of the hills 

 must be attributed principally to the action of the atmospheric forces. 



No one-sided theory, therefore, that should seek to explain all the 

 phenomena by reference to one set of influences alone could be accepted. 



On the present occasion, Mr. J. Geikie could not pursue this subject 

 further. The origin of our mountain and valley systems dated back 

 to much more remote periods than the advent of the Glacial epoch ; 

 and there was nothing more certain than this — that the direction 



