TOPOGRAPHY AND GEOLOGY. 11 



on them in later times squeezes out the clays and shales. The chalk, more- 

 over, is permeated by water, and this accumulates on the clays below, pro- 

 Landslins on viding a lubricated surface for a landslide. The coast 

 ♦Vi r f R /I road of Co. Antrim thus suffers at many spots from 

 tne toast Koad ^j^^ movement of the cliffs above it, notably near 

 01 Lo. Antrim. Garron Point ; and picturesque fallen masses and 

 " undercliffs " result. The village of Straidkilly, on the heights, is noted for 

 the shifting and warping of its buildings, as the ground slips beneath them. 

 Precisely similar phenomena, in the same systems of strata, occur on the 

 coast of Dorsetshire near Lyme Regis. 



At Portrush, the Lias is baked into a flinty porcellanous mass by the 



intrusion of basalt into it from below during the 



Lias of Portrush. Eocene eruptions. It is well seen upon the north 



shore, close against the town, and still retains traces 



of ammonites and other fossils. 



The long period of denudation during Jurassic times was followed by a 

 subsidence, of the north at any rate, during the latter half of the Cretaceous 

 period. Conglomerates and sandstones, true shore-deposits, herald the 

 sea's return. How far the waters spread over central Ireland is quite un- 

 certain, for Cretaceous beds are only preserved under the great outpouring 

 of basalt that covers almost the whole county of 

 White Limestone Antrim. The White Limestone, representing the 

 of Co. Antrim. Chalk of England, is about one-tenth as thick as that 

 of Norfolk, but was deposited in fairly deep water 

 towards the close. The ocean spread westward, as is seen by the odd little 

 outlier of chalk on the northern summit of Slieve Gallion, in Londonderry, 

 now lifted 1,400 feet above the sea. The white cliffs near Portrush, and 

 the beautiful band of white rocks, now coming down to the coast road, now 

 receding far up in the hills, which stretches from Red Bay to Moira in Co. 

 Down, belong to the pure oceanic deposits of the Cretaceous period. The 

 contrast of this gleaming layer, now quarried for lime, with the grim black 

 basalt crags above, is one of the most delightful in the country. Just south- 

 east of Fair Head, above the wooded hollow of Mur- 

 rfu R lough Bay, the chalk forms the summit of the cliff, with 



Murioug Bay. ^ band of coarse conglomerate under it ; the latter 

 was the shore-deposit, laid down when the land sank 

 in mid-Cretaceous times. Beneath this are the far earlier continental 

 layers of the red Triassic sandstone, reposing in turn on a floor of ancient 

 metamorphic rocks, which were probably folded and crumpled by both the 

 Huronian and the Caledonian earth-movements. The Carboniferous sand- 

 stone and the Eocene basalts close at hand complete this " picture in little " 

 of the many changes that the Irish area has undergone. 



The Cretaceous ocean passed away in turn from north-west Europe. The 

 former ooze of the sea-bottom was uplifted as consolidated beds of chalk. 

 The skeletons of siliceous sponges, and other similar remains, had by this 

 time become altered and re-deposited in the mass as bands and lumps of 

 flint. The weather scoured away the soft limestone, and left the almost 

 insoluble flints as pebbles on the surface. Hence chalk downs were formed, 

 comparable to those of Surrey and Sussex, and flint gravels accumulated 

 in their combes and hollows, as they do in the Home Counties of England 

 at the present day. 



On this occasion, the movements were fraught with more serious conse- 

 quences than the mere uplift of a continental margin. As they continued, 



