138 Proceedings of the Royal Irish Academy. 



tiiougli fragments derived fi'om all sorts of Lovrer Silurian, and such. 

 Mnds of rock, form a large percentage of the whole. Pebbles of 

 granite are not uncommon in this gravel, and chalk flints and 

 pebbles are also sometimes present. The lowest of these deposits is 

 found over the northern portion of the district under review, but it 

 terminates at elevations varying from 300 to 400 feet above the sea." 



(p. 67.) — " SliennicJc's Island, oj)jposite Skerries, affords an interest- 

 ing proof of the extreme age of this drift clay. It measures (1860) 575 

 yards in length, from north-west to south-east, by about 150 in width, 

 and is formed of thin gTavelly clay, which the sea has now abruptly 

 escarped on the north-west of the island to the depth of 46 feet. On 

 the opposite shore, south of Skenies, the same deposit is also escarped 

 by the sea, to the depth of 41 feet, the distance between the two 

 "being ia one place close on three-quarters of a mile. This channel 

 has, therefore, been cut by the sea long subsequent to the deposition 

 of this clay, which, no doubt, represents the remains of what was 

 once a very large extent of land stretching into the Ii-ish Sea. The 

 same fact, just noticed, has been mentioned in connexion with Lambay 

 Island, which is two miles and a-half from the nearest point of the 

 mainland, the deepest part of the channel being over five fathoms. 

 The east face of Howth, also, affords us another proof of the existence 

 of land having extended here far into the sea. On the top of the 

 cliffs, from Foxhole to the north of Lough Levin on the south, a 

 distance of 600 yards, we found this brown gravelly clay, containing 

 numerous limestone pebbles, plastered against the rocks, and termi- 

 nating at an elevation of about 100 feet above the sea, having a main 

 width of only 70 yards." 



Enough has been said to prove the gi-eat antiquity of this deposit 

 by the amazing amount of denudation which has taken place since its 

 formation. 



On the shore, one quarter of a mile west of llalahide, there is a 

 layer of gravelly clay, three feet thick and six feet above high- water 

 mark, containing recent shells and fragments of granite, chalk, and 

 flint. At low-water mark there is exposed on the beach east of 

 Malahide, blue marly clay, containing the dead shells of a species of 

 Pholas, &c. 



Memoir of G-eological Survey of Ireland, to sheets 121 and 130, 

 portions of Counties of "Wicklow and Dublin. J. Eeete Jukes, m.a., 

 r.E.s., and G. V. Du2s"oyer (1869). 



(p. 46.) — " The area described lies wholly in the County Tv'icklow, 



