Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/259

 hill, are the edges of beds of chalk covered by basalt, which correspond to beds at distant points which may be seen from the hill- top as in a geological model. The chalk formation here is thinner, and it dips northwards at a low angle. It crops out at the sea-coast, in Lough Foyle, northwards, in Belfast Lough, at Fairhead, and all round a great solitary dome-shaped mountain, Slieve Lude, which rises above Ballycastle. At Slieve Gallion these newer beds rest unconformably upon the edges of older beds, as they do forty miles away at Cushendal. There is nothing in the present surface-forms of these hills to indicate their structure. The chalk and basalts, and the older rocks upon whose edges they were poured out and deposited flat, have been worn away together over a large area in this region for a depth equal to the height of hills at opposite sides and ends of Lough Neagh. The " cap " on the top of Slieve Gallion is a remnant of a great sheet about forty miles square at least ; and rock taken away from hollows since the basalt formed was about 2000 feet deep.

Near the southern end of Lough Neagh and near Dnngannon and Cookstown, the rock-surface is laid bare in quarries. The edges of sandstone beds of the coal-formation are crushed and shattered. Fragments are close to the rock, up in the Boulder-clay, which caps the quarry, together with hard smooth grooved boulders of granite and metamorphic rocks. These last abound at Cookstown, between Slieve Gallion and Dungannon. On the slopes of Slieve Gallion they rise to a height of about 1200 feet. In the low country the drift is packed in long high ridges. Some of the stones came from a distance ; for there is nothing like them in the coal-field.

Southwards, near Armagh, and on the shores of Carlingford Lough, I found scratched polished flints and angular flints, amongst debris of the coal-formation, and basalts, and far older rocks. According to other observers, quoted by Mr. Close, " Antrim Flints " are found in gravels about Bray, near Dublin, and even as far south as Waterford; Mr. Froude brought me flints from Bray. These flints travelled southwards, and did not go northwards. I could find no flints or chalk north of Donegal Bay and Lough Swilly. About 2000 feet of basalt and chalk, of coal-measures, and of older rocks, upon which they were deposited, certainly were crushed, and broken and ground off an area of more than forty miles square about Lough Neagh, between Lough Foyle and Belfast Lough, Slieve Gallion and Fairhead.

Along the sea-coast between Fairhead and Lame, the sea is grinding rocks at the sea-level so as to bring chalk and flints to one polished surface. At a higher level the sea has made a series of caves which can be seen from the road. The same engine has undermined promontories, so that masses have fallen leaving cliffs with talus heaps, and cliffs from which the talus has been removed. In these cliffs the same forms are repeated all the way from Larne to Lough Foyle. They may coincide with faults ; but I could find no faults coinciding with the coast.

Within this area arc the marks of two great " denuding engines."