134 



Froeeedings of the Royal Irkli Academy. 



lower grounds. In the limestone plain, on the north-west, the said 

 rock appears at the surface only in occasional small patches. In 

 the north-east the Glacial deposits overlie the granite less con- 

 tinuously, and patches of scruhby, rocky ground lie amid the 

 fertile drift country. The Eoulder-clay laps round the hills, ceasing 

 at from 500 to 1000 feet. It is often succeeded by sands and gravels 

 (the famous high-level shelly drift of the Dublin mountains), which 

 are, like the Boulder-clay, full of limestone, and are found as high as 

 1500 feet. Above this, rock-debris and peat usually divide the 

 honours between them. It is the distribution of the Glacial deposits 

 that determines the main features of the phytogeography of the area ; 

 and one of the most interesting points of the distribution of the 

 Glacial series is the extension of calcareous clays and gravels far over 

 the non-calcareous rocks, and high up the granite mountain valleys. 



Passing on^to the purely physiographical features of the district, 

 Kippure, 2473 feet, near the southern edge of our map, is the 

 dominating feature — a massive dome, Avith wide peat-covered slopes. 

 Thence a broad ridge, which for several miles maintains an elevation 

 of over 2000 feet, runs northward to Ballynascorney. A few miles to 

 the north-eastward, a parallel broad ridge runs from Prince William's 

 Seat (1825 feet) to Killakee Mountain (1721 feet), approaching 2000 

 feet at several points. jS'orth-east of this again, Two-rock Mountain 

 and its neighbours form a bulky mass, rising to 1699 feet. Between 

 these ridges there are fine mountain glens. The largest of these is 

 Glenasmole, running northward from Kippure, and occupied by the 

 River Dodder. This stream, with its tributaries, is the chief drainer 

 of our area. On emerging from Glenasmole, it runs north-eastward 

 over the low grounds through a trough which it has cut in the drift, 

 to join the sea in Dublin Bay, just at the mouth of the Liffey. The 

 south-western corner of the district drains into the Liffey, which, 

 rising on the south slope of Kippure, enters and flows in our area 

 for a few miles, and, swinging round outside the west and north 

 boundaries of the district, enters the sea at Dublin. The only other 

 stream of importance is the Bray Eiver, branches of which drain 

 south-eastward down the fine mountain valleys of Glencullen and 

 Glencree, the whole stream entering the sea at Bray. The only 

 lakes in the district are two picturesque mountain tarns — Upper and 

 Lower Lough Bray — lying in deep coombs, at an elevation of over 

 1200 feet, on the eastern slope of Kippure, at the head of Glencree. 



The low, drift-covered plain of limestone — the edge of the great 

 central plain of Ireland — that occupies the north-west portion of the 



