On the Geology of the Environs of Dublin. 459 



middle was of an earthy character, darkened by carbonaceous mate- 

 rial, probably that of marine algse. The whole formation was 

 undoubtedly a great marine or oceanic deposit. It was in the first 

 place full of marine shells, the same as those existing in the sea at the 

 present day. Taking a thin section of any specimen of Carboniferous 

 Limestone, however dense and apparently unfossiliferous, let the slice 

 be so thin as to be transparent under a microscope, and they would find 

 it consisted of a mass of shells resembling those of the little animals of 

 the simple forms of life which exist in such vast numbers over the floor 

 of the ocean at the present day, namely, Foraminifera. The Carboni- 

 ferous Limestone was in all about 3000 feet thick, so that the 

 building up of the great organic formation over the floor of the ocean 

 must have taken a period of indefinite duration. When they went 

 to Kilkenny and Cai'low, they found the representatives of the Middle 

 and Upper Carboniferous series analogous to that of the British and 

 Welsh Coal-fields. Professor Hull then proceeded to refer to glacial 

 deposits. No one had contributed more to the elucidation of this 

 subject than the Eev. Maxwell Close. He had shown that the whole 

 of this part of Ireland was at one time covered by a thick sheet of 

 ice, which has left its marks upon the solid rock wherever that rock 

 has been sufficiently protected to prevent the marks being obliterated 

 by time. Those who would be able to be present at the examination 

 of Bray Head on Saturday would have an opportunity of seeing the 

 glacial scorings and groovings upon the surface of the quartzite near 

 Killiney Hill. Drift formations were well represented in the neigh- 

 bourhood of Dublin. They consisted of three divisions. The oldest 

 was Boulder-clay— a formation which disgusted and dismayed engi- 

 neers and contractors, but had furnished a good deal of interesting 

 speculation to geologists. It contained blocks of rock generally 

 glaciated or worn by ice, grooved, and scored. Some of these glacial 

 stones were to be found in the present excavations at Stephen's 

 Green. The stones were not only grooved and scored, but had a 

 polished surface, showing that they had been ground and rubbed 

 over solid rock as the ice was moving along. Undoubtedly the 

 Lower Boulder-clay was the result of the original ice-sheet which 

 covered the whole country, moving in the neighbourhood of Dublin 

 from the north-west towards the east and south-east, and, what was 

 very remarkable, moving through the central plains over the hills 

 which rise between it and the sea, by a force he was not going to 

 speak further of. Let them just fancy that sheet of ice being obliged 

 to pass from the lower ground over such hills as Killiney and Bray 

 Head out towards the sea. The Lower Boulder-clay was succeeded 

 by another series of drift strata, entirely different, consisting of 

 stratified sands, gravels, and marine shells. A beautiful selection 

 of these shells was open for examination at Howth, close to the 

 telegraph-station at the beach, and in half an hour an excellent col- 

 lection of glacial shells of the period might be obtained. These 

 shelly gravels were, of course, deposited under totally different con- 

 ditions from Boulder-clay, which underlay them, because they were 

 evidently deposits which bad been formed in the sea of the period. 



