92 The Irish Naturalist. 



shelly sands at a height of 90 ft. above the sea at Howth and 

 150ft. at Bray; the shells at Finglas are at 200 ft.;' while 

 Mr. Kelly= observed them at 600 ft., east of the north end of 

 Glenismole. Mr. Maxwell Close,^ in one of his most memor- 

 able papers, has given lists of species from much higher 

 elevations. 



Thus, if we follow the mountain-track leading from Rath- 

 farnham towards Glencullen, on the opposite side of the 

 valle}^ to that taken by the main road, we arrive finally on the 

 southern slope of Kilmashogue ; and here, near Calbeck 

 Castle, tough sands and gravels, cemented by carbonate of 

 lime, appear unexpectedly, nestling in a hollow of the hills. 

 In these beds, now much grown over, Mr. Close has found six 

 species of marine mollusca, and this at a height of at least 1200 

 feet. Proceeding over the ridge of Two-Rock Mountain, we 

 descend to the broad col between Glencullen village and 

 Stepaside ; and here, again, gravel covers the granite, and 

 fragmentary^ shells are not at all uncommon. In the old pit 

 opposite Ballj^edmonduff House, Mr. Close discovered the 

 remains of some twenty molluscan species, at a height of 

 almost exactly 1000 feet. This pit has now fallen in and is 

 grass-covered ; but the stratification of the gravels is well 

 seen in Mr. Dunne's pits 100 feet or so higher up the road, 

 where shells, in fragments about 5 mm. across, may easily be 

 obtained by sifting."* 



The finest section of these "sands and gravels," probably 

 one of the grandest in the British Isles, occurs on the banks 

 of the Cookstown River, where Glencullen narrows, some two 

 miles up from Enniskerry (Plate i.). Here the valley has 

 evidently been choked with "drift" material, and the stream 

 has cut its way down through it, and in places has reached the 

 granite bed. The characters of the deposit here are the same 

 as in other parts of the county. The sand consists of quartz 

 and mica, possibly with some flint particles. The larger 

 blocks are of very varied nature ; granite boulders, abundant 

 Carboniferous limestones, chert. Cretaceous flints, Ordovician 

 igneous rocks like those of Tallaght and Lambay, quartz- 

 masses, and schists from the contact-zone of the granite — 

 these are all mingled together, some fairly rolled, others 

 merely subangular. The percolating waters have dissolved 

 portions of the limestones, and have in other layers firmly 

 cemented the blocks together by redeposition of the carbonate 

 of lime. 



^ Oldham, G. S. D., iii., 66. 



2 " The Drift of the district about Rathfarnham," G. S. Z>., vi., 144. 



3 "The Elevated Shell-bearing Gravels near Dublin," G. S. /., iv., 36; 

 and Geological Magazine, 1874, p. 193. 



^ Dr. Oldham wrote in 1844 {G.S.D., iii, 70), " I have never yet failed to 

 find fragments, at least, of shells, wherever I found clays, hard, close, 

 blueish, gravelly clays with the gravel." This applies to the whole 

 counties of Dublin and Wicklow. 



