182 THE RIVER VALLEYS OF 



that action combined with glacial and marine denu- 

 dation, and that all were generally led by the breaks 

 and faults in the rocks. 



S.W. Cork, as also most, if not all of Ireland, 

 during the "Esker-sea" period, was relatively about 

 350 feet lower than at present, which is proved by 

 the raised beaches, terraces, and the like, found in 

 various places. 1 Such a change of level would lay 

 most of the valleys of this country awash, and place 

 them in such a position from currents and tidal- 

 waves, that the sea would have the opportunity of 

 doing more work than at present. And that the 

 Esker-sea did a considerable portion of the denuda- 

 tion seems probable, as the rivers that now occupy 

 the valleys since the retirement of the sea have not 

 been able to clear out the great mass of sea-formed 

 detritus, the result and evidence of marine denuda- 

 tion, consisting partly of Esker gravel, partly, per- 

 haps, of estuarine deposits ; even the old terraces and 

 bars of the Esker-sea remain, in places, nearly intact. 



Before, and during part at least of the " Esker-sea " 

 period, the mountains in South-west Ireland were snow- 



1 Since this was in press, our colleague, Mr J. Croll, in one of his 

 able papers, has shown that as the northern ice-cap advanced or re- 

 treated, the level of the sea oscillated, while the land probably remained 

 stationary. This will account for the very uniform altitude of the 

 ancient sea-beaches ; thus removing a great stumbling-block, for if the 

 land had been elevated, the movement scarcely could have been equal 

 everywhere. Ancient beaches now found at exceptional heights, pro- 

 bably point to real movements in the land's surface due to local dis- 

 turbances. 



