Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/261

 which appear as spots upon the Mountain-Limestone in geological maps.

After seeing the destruction worked upon Dungannon sandstones, and the denudation of regions about Lough Neagh and Lough Erne, it is also seen that engines able to do such work may have destroyed coal-formations over the whole area of " denuded" Mountain-Limestone in Ireland. But if they did, then the low grounds are chiefly hollows made by the same engines which destroyed the Antrim chalk and Sligo limestone. Weathering and rivers could not and did not do this work, which I attribute to ice and the sea.

VIII. Valentia. — At the other end of Ireland, at Valentia, near the telegraph station, is a bank of Boulder-clay scarped by the sea. Slate rocks have there been crushed, smashed, and ground to powder. Chips remain in the clay so arranged as to prove that the engine which here crushed the solid rock came from the mainland down certain deep glens, split on Valentia Island, and went seawards on both sides of the island.

An instantaneous photograph of withered leaves caught up and whirled along by a strong wind might give some notion of the arrangement of chips of slate in the clay at Valentia. But in the immediate neighbourhood are finely polished, hard, grooved slate rocks, which prove that a great stream of heavy ice passed into Dingle Bay, moving north-westward after it split on Valentia Island and crushed the softer slate. The other half of this stream went to sea westwards.

IX. Ice and the Sea. — At these three places, about Lough Neagh, Lough Erne, and Valentia, the destruction of rock is recorded, as the quarrying of slate is at Valentia and at Bangor, by remnants left standing in quarries. At these three places marks of glacial action upon a very large scale abound, and extend vertically from the highest tops to the sea-level. But these glacial marks upon the surface commonly end abruptly at the brink of tall cliffs, which the sea is undermining and has undermined.

Off the south-west coast, far out at sea, tall peaks and scarped rocky fragments, the same in all particulars as rocks in neighbouring points, stacks, rocks, and needles, out to the Skelligs 700 feet high, are monuments of havoc wrought by the sea, after the ice-engine had struck work. Upon these outliers all the power of waves and weather now spend their utmost force ; and the effects are manifest in cliffs at all the exposed points in the south-west. It is easy to see that Irish rocks have been greatly worn from above, and that ice did a great deal of the grinding. It is plain that the sea now is destroying the land by undermining it. The shape of Irish lands and coasts I attributo chiefly to the working of these two engines, ice and the sea.

X. Glaciation. — Glacial marks can best be seen amongst bare rocky hills, where rock-surfaces are most exposed, and where the shape of glens and hills, which arc grooves and ridges in the solid, can best be distinguished from piles of loose drift. The structure of hills can