CoLK — The Problem of the Liffeii Valley. 11 



the well-known waterfall descends. The ground of the Powerscourt demesne 

 is heavily buried in glacial drift, thi'ough which the river now cuts its way. 

 Its unseen floor of rock coi'responds with the mature plateau of Eoundwood, 

 though cut down to a lower level. At it.s foot, about Tinnehinch, we drop 

 .suddenly into the region of ravines. 



Further north, the small Carriekmines Eiver,. rising on Three Eock 

 Mountain, occupies a broad mature valley above Carriekmines, in the floor of 

 which it cuts the abrupt notch of Gleudruid, where it drops towards th e low 

 ground of Loughlinstown on a rock-slope of 45°. This steep hollow, cut in 

 the granite, and set with little waterfalls, repeats the features that are 

 exhibited on a bold scale by the Dargle and the Devil's Glen. Glendniid 

 starts, however, onh' 220 feet above the sea.' 



The Vale of Ovoca has been overdeepened, and the curve of the earlier 

 broad upland basin is traceable when we look across it from above the mines 

 of Ballymurtagh. The river here runs below us between two con-spicuous 

 cHifs, which probably give a measure of the overdeepening. Numerous 

 other instances might be cited, such as the uplifted peneplane of the Tramore 

 coast, to show that the surface of south-eastern Ireland lay much nearer sea- 

 level in late Cainozoic times, and that the streams became rejuvenated by 

 uplift somewhere before the Glacial epoch. If, as is here suggested, the Slade 

 of Saggart was cut by water descending from the Leinster Chain, its relati^'e 

 lack of maturity finds a parallel in the Dargle valley and the Devil's Glen, 

 and is no doubt due to the same causes. 



There are obvious difficulties in the above explanation of the preservation 

 of the lower slopes from stream-action until almost recent times. The 

 subsidence required to protect them would have admitted the sea over the 

 Irish lowlands to so wide an extent that Cainozoic marine deposits ought to 

 be common beneath the boulder-clay. These, however, would have been 

 largely removed by glacial scour, and such relics as remain may be those that 

 are buried most deeply and successfully in the drift. Mr. James Brenan, of 

 Ballinabrauagh Xational School, Carlow, has recently called my attention to 

 the occurrence of marine fossils of a decidedly Pliocene aspect, including 

 Pectunculus and Fusus, in fields 5 miles south of Carlow and some 500 feet 

 (150 m.) above the sea. Mr. T. Hallissy, who has investigated this discovery 

 on behalf of the Geological Survey, reports that the shells lie in a surface-soil 

 derived from boulder-clay. There is no likelihood that they ha^■e been brought 

 for manuring purposes into a region rich in limestone, and the fact that their 



' Jlr. J. E. Kilroe has pointed out that Glendruid was atleast partly excavated in pre-Glacialtimes. 

 ' Geology of country around Dublin," Mem Geol. Surv. (1903), p. 117. 



