150 The Irish Natttralist. 



THE HIGH AND LOW-LEVEL SHELLY DRIFTS 

 AROUND DUBLIN AND BRAY. 



BY T. MEU.ARD READE, F.G.S. 



( Cone hided from page 121). 



It is now time to get to the piece dc resisla?ice — the shelly 

 gravels of the Three Rock Mountain, first disclosed to the 

 scientific world by the Rev. Maxwell Close. I am specially 

 interested in these deposits from a previous study of similar 

 gravels in England and Wales. We examined the gravel pits 

 at Ballyedmonduff, reached by us from Glencullen. They are 

 evidently continuously connected with the valley drift, and 

 these high-level gravels occupy a considerable area. The 

 gravel is mostly of limestone,, with a good proportion of 

 granite boulders, also felstone, porphyry, Silurian grit, and 

 purple conglomerate. The gravel is interbedded with sand, 

 loamy sand, and sand and gravel. Some thin contorted bands 

 of sand are to be seen. Shell fragments are common. No 

 attempt was made at collection ; and for a list of the species 

 of mollusca found, the reader must refer to Mr. Close's 

 original paper in the Geological Magazine, 1874, entitled 

 " The Elevated Shell-bearing Gravels near Dublin." 



A mechanical analysis of two specimens of the finer part 

 of the drift showed that the finer gravel was well worn, and 

 mostly limestone, mixed with sub-angular gravel. Some pieces 

 of black limestone occurred, very polished and slightly striated. 

 Among the smaller grains were well rounded and polished 

 grains of quartz, also calcite, mica flakes, and very decayed 

 grains of shell substance. Three minute siliceous cylindrical 

 bodies were found in this material, and similar bodies occurred 

 in other specimens of the drift from several localities, as well 

 as in the Greenhills esker, at Balrothery, presently to be 

 described. Dr. George G. Hinde, F.G.S., to whom these 

 were submitted, pronounces them to be sponge-spicules. He 

 writes : " They are for the most part portions of the long 

 cylindrical spicules, of which the anchoring ropes of hexacti- 

 nellid sponges, like the still existing Hyaloncma, were com- 

 posed, and they are the sponge remains most commonly 

 present in Carboniferous cherts and limestones in Britain." 

 The analysis disclosed the fact, that there was a considerable 



