Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/258

 removed from hollows and from low grounds in Ireland is manifest. The excellent maps and sections of the Geological Survey, by showing what is left, prove that a great deal has been removed ; but this can best be seen on the ground.

VI. In Antrim the hills left were shaped out of a late geological formation, which was spread over a wide area between Mull and Deny. At Red Bay, near Cushendal, in Antrim, at the sea-level, the rocks washed by the sea are coarse red-sandstone beds dipping about S.E. at a steep angle. I believe them to be New Red Sandstone. Their strike extends inland S.W. In that direction the broken edges of the beds of sandstone are covered unconformably by nearly horizontal sheets of igneous rock, upon which rest beds of chalk, which are covered by more sheets of igneous rock and ironstone. From marks which I found amongst these igneous rocks, it is certain that they were fluid and flowed as lava does, or the slag from a furnace. The basalts of the Causeway and elsewhere are columnar, like the rocks which flowed out of Sn Befell, in Iceland *.

The chalk contains flints and fossils ; and it certainly was deposited horizontally at the bottom of the sea, over a wide area. This whole threefold series still lies nearly flat, or slightly inclined, upon the sandstone edges which strike under the Antrim hills. This is an old surface of denudation buried under newer rocks.

The region has been faulted and has been undermined by waves, so that cliffs abound along the coasts ; but it has also been ground and "worn from above, so that iron ore and chalk crop out at points widely separated and at different levels. In crossing the Antrim hills, ironstone workings in the edges of flat beds appear on the turf of rounded slopes, on opposite sides of glens and hills and " cols."

They show that hollows have somehow been grooved out of flat beds of chalk and basalt, whose thickness can be measured along the escarpments next to the sea. From the hill-tops to the sandstones is somewhat less than 2000 feet ; and that is a vertical measure of solid rock which has been taken away in shaping the Antrim glens and the Antrim hills, since the upper basalt was formed.

Westwards from the Antrim hills, on the other side of Lough Neagh, at about 40 miles from Red Bay, is a hog- backed ridge called Slieve Gallion (Mount Storm). The long axis of this ridge runs about north and south ; it is about 1800 feet high, and it may be eight or nine miles long. It is the most conspicuous hill in the region. Up to 1200 feet the base of this hill is sprinkled or thickly covered with the drift, which also covers all these low grounds. Above the level of the drift it is easy to see that the bare body of Slieve Gallion is made of beds of hard stratified metamorphic rocks, dipping about northwards at a steep angle, and striking westwards through the ridge. At the northern end, capping this

groups of hills scored horizontally by ice. The problem is, whether the Irish hollows ever were filled with solid ice ; if so, to what height the ice-level rose, and how far the ice-field extended during the last glacial period.


 * Rubbings and specimens of igneous surfaces were shown in illustration.