2l8 



THE BRITISH NATURALIST. [September 



moraine is visible to this day. Possibly in the earlier periods of the 

 glacial era the main body of the Reeks Glacier flowed in a N.E. 

 direction, and then impinging on Tore was diverted towards the west 

 by that mountain, and by the general set of the Arctic currents until 

 the parent and the infant glaciers joined forces once more. But in later 

 times of shrinking and retrocession the Gap Glacier ended as I have de- 

 described, and the only union would be that of the effluent streams of the 

 two. If the practical result of such a circle of drainage be the washing away 

 therefrom the droppings of the glacial ocean, another effect must also be 

 considered. In the post-glacial changes of the last 200,000 years, more 

 or less, the exposed limestone must have suffered a considerable 

 abstraction from its bulk which the strata outside the sphere have 

 escaped. Free scope must have been afforded to the ordinary denuding 

 agencies in their action on the uncovered rocks of the locality. When 

 we note the limestone as it emerges from its mantle of 80 yards thick 

 and compare its fresh, bluish grey, and crystalline texture with the 

 bleached and worn appearance of the fragments below, whether 

 islands, or peninsulas, or scattered cliffs, or pinnacles hidden amongst 

 dense masses of foliage, we are able to appreciate to the full the pre- 

 servative power exerted by the drift. 



Under the drift the greatest denudation that can go on is that effected 

 by the solvent power of acidulated water. We may take it for certain 

 that here, as in all other carboniferous limestone strata the channels 

 of drainage are becoming gradually enlarged from chinks to caverns, 

 the roofs of which in time will disappear, and narrow valleys result. 

 The phenomenon of an underground rivulet bursting out in full stream 

 into the open air is seen at Muckross, as in the other mountain lime- 

 stone districts — Malham Cove, Gordale Scar, Ham, and Bakewell — it 

 has in the chalk and other water lime formations. I remember well on 

 examining strata in Sutherland that are at least pre-Silurian, if not pre- 

 Cambrian, how I seemed to recognize an old friend in the gush by 

 many heads of an abundant stream, out of a bed of perhaps the earliest 

 known limestone in these isles, if not in the whole world. 



Behind the Muckross Hotel is a patch of swampy ground, where the 

 drift ends and the limestone emerges, where a mill pool has been 

 formed by damming the water which rises from the underground in 

 many little springs and which in some places may be seen raising the grey 

 mud at the bottom in never-resting little heaps. The mill has been 

 removed, but the dam remains, and the overflow is a stream of 

 brilliantly clear water, the sight of which is most refreshing to the 

 person who comes from a country where pollution of rivers is the 

 universal practice. The stream is chokeful of green vegetation, great 

 aquatic plants rising out of it, and long waving weeds swaying 

 forever from side to side in the current, and yet no tinge of discolora- 



