James Geikie — Denudation in Scotland. 25 



After referring to the proofs of this waste, Mr. Geikie went on to 

 remark that a study of the valleys in which the kaims had been thus 

 denuded would convince the geologists that in former ages our rivers 

 must have greatly exceeded in size their present representatives. 

 The position of some of the older alluvia, and the evidence of river 

 action in places to which streams of the same size as now flowed in 

 the valleys never could have attained, all led to this inference. He 

 thought it extremely probable that it was during the age of forests, 

 when Britain formed a part of the continent, that our rivers reached 

 their greatest development. There were good grounds for believing 

 that at this period glaciers filled some of our higher valleys. In 

 some of the high level river gravels, also, we often met with large 

 boulders, which appeared to have been ice-borne to their present 

 position. And the testimony derived from the nature of the timber 

 dug out of the peat-mosses was quite in harmony with such a sup- 

 position. For the climate that nourished the large pine-trees of the 

 English mosses must have covered our rivers with ice in winter. 

 While this excessive climate prevailed, atmospheric waste, no doubt, 

 went bravely on ; and even down to much later days, when the peat- 

 mosses were increasing and the ancient forests decaying, the work of 

 denudation must have proceeded more rapidly than now. 



Some examples of post-Glacial waste were then cited. He men- 

 tioned the case of the gorge through which the Kiver Doon makes its 

 way after escaping from its parent lake. In cutting out this ravine, a 

 mass of rock, equal to at least 70,000,000 of cubic feet had been re- 

 moved bodily by the stream ; and many similar cases might be adduced. 

 But although, locally considered, the denudation thus experienced by 

 drift deposits and subjacent rocks might be often great, it would re- 

 quire a far longer lease of time than had elapsed since the close of 

 the Glacial epoch ere the characteristic features impressed upon our 

 hills and valleys during that period could be effaced. In conclusion, 

 he said they could not fail to be impressed with one consideration, 

 which, above all others, seemed to stand out prominently after a re- 

 view of such matters as they had been that evening considering — 

 and that was the enormous time required to produce the broader 

 effects of denudation. How many long ages had rolled away since 

 these islands rose above the level of the Arctic Sea in which our 

 marine drifts were amassed, and yet, during all that time, how little 

 change had come upon them at the instance of the atmospheric 

 forces. And if the records of the old Arctic condition — the deli- 

 cate ice-markings on the rocks, the loose incoherent deposits on the 

 hill-slopes and plains — still remained so perfect, notwithstanding 

 the ceaseless activity of the denuding agents — if the mere skin as it 

 were, and surface -markings of the land were still so largely retained, 

 what should we say to the time required for the growth of that 

 covering itself, and for the production of these strange ice-mouldings 

 and flutings, — and how, above all, could we apprehend (for compre- 

 hend we could not) the truly tremendous lapse of time, during which 

 the solid land was gradually sculptured into hills and valleys b}'- the 

 rains and frosts and rivers of the past. — The Glasgow Herald, No- 

 vember 30, 1867. 



