1

tions by land-ice. But the majority of the Irish geologists believe that, after the epoch of the Lower Boulder Clay, the land gradually sank until the depression, during the time when the Middle Sands were deposited, amounted in some places to at least 1500 feet. It was then again slowly raised. The temperature, which had been higher during the submergence, again declined (though whether the fall in it was wholly due to the rise of the land is uncertain), so that glaciers once more occupied the mountain valleys, and perhaps descended sometimes to the sea-level. short, the opinions which hitherto have been generally entertained as to the glacial history of Ireland agree in the main with those held by Sir A. Ramsay in regard to Great Britain.

In

In Ireland also scattered erratics occur, though they appear not to be dispersed in such regular streams as in Great Britain. They belong, in some cases, to a late stage in the history of the Glacial Epoch; but Ireland exhibits a more extraordinary series of kames or eskers than any other part of the British Isles. Groups of these extend across the great central plain from the south of Galway to the neighbourhood of Dublin, and as far north as the valley of the Laggan on the borders of Down and Antrim.2 Near Parsonstown they are more or less

1 The writer has seen but little of the Irish boulder clays except in counties Dublin and Wicklow. There they commonly exhibited some indications of stratification, and appeared to pass up occasionally into gravels and sands.

2 Hull, ut supra, chap. v.

ridge-shaped, occasionally roughly parallel, enclosing hollows, sometimes almost circular, sometimes elongated, but now and then spreading out into knolls or shoulders. On the southern side of the broad valley of the Shannon, as, for instance, in the neighbourhood of the ancient sanctuary of Clonmacnoise, they form a line of hills in outline curiously resembling moraines. These are sometimes quite narrow at the top, but sometimes a fair breadth. Here and there an insulated hill may be seen; but generally they form a range, and occasionally the main line has a "backing" of lower mounds. The stones are

mixed with fine gravel and coarse sand; they are commonly subangular to fairly rounded, ranging from about 4 to 10 inches in diameter, but occasionally much larger blocks occur, generally more angular in shape. The materials seem water-worn rather than ice-worn, and not infrequently are distinctly stratified. These hills, in short, are gravel-banks rather than moraines. In this part of Ireland most of the pebbles are a dark limestone (Carboniferous), but Palæozoic sandstones and grits also occur, with various crystalline rocks, such as a diorite and granites (reddish). Professor Sollas, who has paid much attention to these curious accumulations, informs me that the maps of the Geological Survey prove them to bear a certain relation to the general drainage system of the country, and that they converge in groups like those of stream-courses. That

they can be moraines seems impossible; it is difficult to understand how they can have been deposited either by currents in a sea or by the direct action of rivers; in short, the exact mode in which they have been formed, as already stated, is one of the unsolved problems in geology.

CHAPTER III

ICE-WORK IN EUROPE AND OTHER PARTS OF THE WORLD

THERE can be no doubt that Scandinavia, during parts at least of the Glacial Epoch, was almost buried beneath ice, but it is less certain how far southward

this extended. Drifts, however, in some way of glacial origin, can be traced, speaking in general terms, to the fifty-first parallel of latitude. Some of

the most remarkable sections occur in the island of Möen,1 displayed in cliffs from 100 to 400 feet high. The chalk-like that of Norfolk-is overlain by the following deposits:-(1.) Stratified loam and sand (about 5 feet thick), containing occasionally marine shells, sometimes having a breccia of flint at the base. (2.) Unstratified blue clay, with small pebbles and fragments of Scandinavian rocks-20 feet. (3.) Unstratified yellow and more sandy clay, with pebbles and boulders (angular) from the same source--40 feet. (4.) Stratified sand and gravel, with occasional large erratics; this varies in thick

1 Described by Sir C. Lyell, "Antiquity of Man," chap. xvii. See also Professor J. Geikie, "Prehistoric Europe," chap. x.