1862.] JVKES — ^RTVER-VALLEtS. 399 



Soon after the commencement of this action of disturbance, the 

 Coal-measure beds that were over those points or lines which were 

 most bent upwards rose in consequence above the sea, and suffered 

 denudation by its waves. This action went on until the whole 

 country, and probably a much wider district than Ireland or even 

 than the British Islands, was raised into dry land, and its upper 

 portions partially destroyed during the process. 



All this took place, and probably a considerable amount of atmo- 

 spheric denudation also, before that subsequent partial depression 

 of the British area which brought it down again beneath the sea, in 

 which the Permian and IS'ew Eed Sandstone beds were deposited. 



No part of Ireland, except the north-east quarter, suffered from 

 this depression, sufficiently, at aU events, to be brought beneath the 

 sea, either in the Triassic or any other period except the Glacial or 

 Pleistocene. 



The surface left by the original marine denudation was considerably 

 above the present one, and the upper part of the limestone especially 

 was far more extensive then than it is now. The Coal-measures, 

 which now form high lands, were then valleys in the hollows of 

 higher limestone ground, the beds of which, of course, always dip 

 towards the Coal-measures ; and the general level of this limestone 

 country was above the level of the old depressions in the Silurian 

 rocks over Killaloe, over Graiguenemanagh and St. Mullins, over 

 Inistioge, and over Waterford. 



The Shannon, the Barrow, the Nore, and the Suir, when the 

 original rivers first began to run over this high surface, sought of 

 course the lowest levels that then existed for their courses, and those 

 lowest levels were nearly above the lines of their present channels. 

 The Nore ran across the Coal-measure valley, which was then in the 

 ground over Abbeyleix and Kilkenny. The ridge over the Knock- 

 mealdowns was high enough to deflect the Suir ; and the gaps at 

 either end of the Galty group did not then exist, but were occupied 

 by high limestone ground. High limestone ground also separated 

 the basins of the Liffey, the Barrow, the Boyne, and the Shannon ; 

 and the high limestone ground of the Burren of Clare was then con- 

 tinuous over the adjacent parts of Galway, rising stiU higher over the 

 Slieve Aughta and over the Granite on the north side of Galway Bay. 



The rivers trenched this higher surface nearly above their present 

 courses, running then with a more rapid and powerful stream than 

 they do now ; and as the whole country slowly wasted and sank 

 under the wearing influence of the weather, their streams were strong 

 enough always to cut their channels downwards, through whatever 

 rocks became exposed, faster than the general degrading influences 

 could lower the general surface of the country, although those general 

 influences lowered the limestone country to a greater extent than 

 they were able to lower the country composed of other rocks which 

 the river- channels traversed. 



It is remarkable that the limestone-shale ground immediately at 

 the foot of the Old Red Sandstone and Lower Silurian ridges is often 

 lower than the limestone ground beyond. I attribute this to the 



