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II. 



THE PEOBLEil OF THE LIFFEY VALLEY. 



By GEEXVILLE A. J. C'lJLE. M.K.I A.. E.G.S.. 

 Professor of Geology iu the Eoyal College of Science for Ireland. 



PLATEJ> I-III. 

 Bead Jc.ve 24. Published Acgist 21, 1912. 



The Course of the Liffey in the Uplands. 



The Liffey rises in the county of Wicklow. on the south side of Kippure, at 

 about 1,700 feet (530 m.) above the sea, and is joined in the upper part of 

 its course by the Lugnalee, Ballylow, and BaUydonnell Brooks, all descending 

 as consequent sti'eams from the north-west slope of the '•' Caledonian " granite 

 range of Leinster. Xear Kilbride^ the river, now meandering in a considerable 

 flat of glacial drift, tiuiis to the south-west, and joins the Kings Elver at 

 Baltyboys House, south of Blessington. The Kings Eiver, rising in the 

 great moorland at Wicklow Gap, has already attained far more importance 

 than the Liffey, which unites with it on a drift-platform, almost at right 

 angles (Plate XL, fig. 1). The course of the Kings Eiver to this point runs 

 practically parallel with that of the Liffey between Kippure and Kilbride. 

 Both are obviously consequent streams. Their united waters, however, known 

 as the Liffey, are diverted almost immediately to the south and south-west, 

 and have excavated a fine rock-gorge iu which the waterfall of PoUaphuca is 

 a striking incident (Plate II, fig. 2). Below this gorge the LifliBy meanders, 

 far out of its direct course to the sea, along the margin of the Bog of Allen 

 in the drift-covered central plain of Ireland. 



The course of the Dodder, rising close to tlie Liffiey, but on the north side 

 of Kippure, remains far more dii-ect, and the contrast between tlie two rivers 

 has been often pointed out. 



The Tallets at Beittas. 

 The bend in the Liffey at Kilbride appeal's the first anomaly in its course. 

 As the river entei-s the drift-filled area, a broad highly matured valley 

 stretches before it to the Slade of Saggart; the Slade is a steeper vaUey 

 descending northward over the upland edge. The rise in the present drift- 

 filled floor of the valley that leads upwards fi'om Kilbride is only 130 feet, 



