president's address. 19 



distance from and a few dozen feet below the rocky summit of the 

 hill, being about 1,300 feet above the level of the sea and at least five 

 miles from its margin. About fifty-five species of molluscs and twenty- 

 three of foraminifers have been identified. According to the late Dr. J. 

 Gwyn Jeffreys, 1 the majority of the molluscs are littoral in habit, the 

 rest such as live in from ten to twenty fathoms of water. Most of the 

 erratics have been derived from the Welsh mountains, but some rocks 

 from Anglesey have also been obtained, and a few pebbles of Lake 

 District and Scottish rocks. If the sea were about 1,300 feet above its 

 present level, Moel Tryfaen would become a small rocky island, open 

 to the storms from the west and north, and nearly a mile and a half 

 away from the nearest land. 



I must pass more rapidly over Ireland. The signs of vanished 

 glaciers — ice-worn rocks and characteristic boulder-clays — are 

 numerous, and may be traced in places down to the sea-level, but the 

 principal outflow of the ice, according to some competent observers, 

 was from a comparatively low district, extending diagonally across the 

 island from the south of Lough Neagh to north of Galway Bay. 

 Glaciers, however, must have first begun to form in the mountains on 

 the northern and southern side of this zone, and we should have ex- 

 pected that, whatever might happen on the lowlands, they would con- 

 tinue to assert themselves. In no other part of the British Islands are 

 eskers, which some geologists think were formed when a glacier reached 

 the sea, so strikingly developed. Here also an upper and a lower 

 boulder clay, the former being the more sparsely distributed, are often 

 divided by a widespread group of sands and gravels, which locally, as 

 in Great Britain, contains, sometimes abundantly, shells and other 

 marine organisms; more than twenty species of molluscs, with fora- 

 minifers, a barnacle, and perforations of annelids, having been 

 described. These are found in counties Dublin and Wicklow, at various 

 altitudes, 3 from a little above sea-level to a height of 1,300 feet. 



Not the least perplexing of the glacial phenomena in the British 

 Isles is the distribution of erratics, which has been already mentioned 

 in passing. On the Norfolk coast masses of chalk, often thousands 

 of cubic feet in volume, occur in the lowest member of the glacial 

 series, with occasional great blocks of sand and gravel, which must 

 have once been frozen. But these, or at any rate the larger of them, 

 have no dcubt. been derived from the immediate neighbourhood. Huge 

 erratics also occasionally occur in the upper boulder clay — sometimes 

 of chalk, as at Roslyn Hill near Ely and at Eidlington in Eutland, 

 of Jurassic limestone, near Great Ponton, to the south of Grantham, 



1 Quart. Journ. Oeol. Soc, xxxvi. (1880), p. 355. 



' See T. M. Reade, Proc. Liverpool Oeol. Soc, 1893-94, p. 183, for some weighty 

 arguments in favour of a marine origin for these deposits. 



c2 



