112 G. H. Kinahan — On Denudation. 



Other extreme subserialists would make their favourite agencies do 

 an enormous quantity of work ; and to prove these theories they 

 base their calculations on the fallacy : " That all the surface of the 

 ground is being more or less denuded." This, however, is contrary 

 to facts. In tropical regions there must be an enormous amount of 

 denudation, as the hot winds and sun parch up the surface, forming 

 great thicknesses of debris, to be carried away by the torrents during 

 the subsequent rains. Still, even in those climes, denudation does not 

 affect the whole area, as miles are covered with jungle and forest, 

 sure protectors of the surface. In alpine and arctic regions the 

 everlasting snow and ice act in a similar manner, and it is question- 

 able if in the temperate regions, the chemico-fluvial agencies are able 

 to gradually denude even half the surface exposed : for in damp dis- 

 tricts undoubtedly they imhirally would act more as preservers than 

 destroyers. This is well exemplified in many mountainous mining 

 districts ; for in such localities fuel is often scarce, and the miners 

 out for firing all the peaty surface soil that clothed the mountain and 

 preserved it from denudation ; consequently the rain and other 

 agencies act upon it for a season, cutting the surface into small 

 ridges arid hollows. Nevertheless this does not last long, as the 

 dampness of the climate soon clothes it afresh with a peaty garment, 

 and thereby effectually preserves it. In a district miners have 

 occupied for a considerable time, all the different stages can be 

 observed. The places from which turf has not yet been cut, where 

 there has been no denudation : the newly turf-bereft sj)ots, where 

 denudation is at work ; and the older turf bogs where the mountain is 

 again covered with a thin coat of peat. 



A group of table-topped hills, capped by peat and bounded by 

 steep escarpments, are good illustrations, showing the contrast 

 between the destroying and preserving powers of the chemico- 

 fluvial agencies. First the original mass, by denudation of some 

 kind or another, would seem to have been planed into a flow- 

 ing gradually undulating table land with gently sloping sides. 

 Subsequently, by one or other of the kinds of denudation, or what 

 is more probable, by two or more combined, valleys and ravines 

 were cut transversing the table land in various directions, 

 and forming the individual hills. When the chemico-fluvial 

 agencies began to work, or a short time afterwards, peat must have 

 begun to grow on the hill tops which effectually prevented them 

 from being denuded, therefore those powers could only act in the 

 valleys and ravines, on the sides of which they formed steep 

 slopes, crowned by perpendicular escarpments usually a few feet 

 higher than the thickness of the envelope of peat. The thickness 

 under the peat is generally the remains of the original surface 

 drift of the ancient undulating table land, and as the covering of 

 peat now protects its surface, the chemico-fluvial agents work in 

 sideways, undermining the peat, which consequently topples over 

 in large pieces when its weight overcomes its tenacity. Thus, 

 as the waste is proceeding both vertically and horizontally, the area 

 of the flat summits must decrease, although most slowly. Favour- 



