James Geikle — Denudation in Scotland, 19 



the weather seems to have the power of removing the bhie part of 

 the colouring matter." In my notes on the rocks of the Co. Galway, 

 I find : " The original colour of the Felsite associated with the granite 

 on the north of Galway Bay seems to be a purplish green or grey, 

 but at the coast they weather red, while inland they weather a 

 yellowish or dirty white." 



On the disintegration of rocks has been noted — ''At the sea-shore 

 south of Baltimore, Co. Cork, the slates immediately above the in- 

 fluence of the waves have by the weathering out of their slaty 

 cleavage become so rugged and sharp that they can be compared to 

 nothing but knives placed side by side with their edges looking up- 

 wards ; this appears to be remarkable, for if these rocks are followed 

 only a little inland, they seem scarcely weathered as the ice striae are 

 quite perfect on them." " The slates composing the Little Skellig, 

 off the coast of Kerry, are weathered along the nearly vertical cleav- 

 age planes, giving them a sharp serrated surface, while similar rocks 

 on the main land only a little removed from the sea-coast are scarcely 

 weathered." 



" On the Aran Islands, Galway Bay, the subaerial agencies seem 

 to denude the limestones quicker than on the mainland, for on those 

 islands the perched blocks having protected the portion immediately 

 under them, now stand on pedestals from four to six inches high, 

 while inland, the pedestals under the blocks rarely exceed four 

 inches, and generally their average is about two inches and a-half." 



" The veins of Eurite that traverse the Granites on the north of 

 Galway Bay, are scarcely affected by the weather, and thereby give 

 a record of the amount of waste the mass of the granite rocks have 

 undergone since the ice disappeared from that country. From them 

 it would also appear that the granites disintegrate more freely near 

 the sea than away from it ; for inland these veins stand from half 

 an inch to two inches above the mass of the rock, while near the 

 sea they have been remarked as much as three and a-half inches, 

 and rarely, if ever, are less than an inch and a-half ; moreover in. 

 some places near the sea, even the Eurite veins are weathered." 



I. — On Denudation in Scotland since Glacial Times. 



By James Geikie, Esq., of the Geological Survey of Scotland. 



[Being the substance of a paper read before the Geological Society of Glasgow, 

 28th November, 1867.J 



MR. JAMES GEIKIE began by remarking that, throughout the 

 wide domain of Geological inquiry, there was perhaps no sub- 

 ject of M^hich it was easier to gain some idea, and yet, at the same 

 time, more difScult to acquire an adequate conception, than denudation. 

 We all know how rains and frosts and chemical decomposition were 

 employed unceasingly in modifying the aspect of hills and plains, — 

 how rivers were ever deepening and widening the valleys in which 

 they flowed — how the sea, by its constant wave-action, aided by 



