Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/263

 out to sea. The landward sides of these hills are all rounded, curved, glaciated rock- surfaces, weathered or well-preserved, on which are drift-ridges, sheets of drift, moraines in perfect preservation, and all other marks of glacial action.

The ice-engine has ceased to work ; but the tool-marks and chips are there about Carrick.

The seaward sides of these hills are marks of the sea, which is still at work in full power.

The sea is undermining these hills : they have long been undermined by the sea ; and one side of Slieve Liag has been removed. The highest top is close to the verge of a broken escarpment nearly 2000 feet high, facing the Atlantic. To look up from a boat is to understand the working of the sea upon a coast. At several places at the base of cliffs are beautiful white beaches of hard rounded pebbles arranged in the usual sweeping curves. At high- water-mark these pebbles, driven by all the force of Atlantic waves, have hollowed a groove in hard white quartz rock, some four or five feet high, of varying depth, and parallel to the water-line. The rock-surface is smooth as polish can make it, as smooth as glaciated vein-quartz on the other side of the hill ; but the form of this surface is quite different. It is not grooved and striated in parallel directions by stones and mud fast in ice, moving steadily down in one broad continuous sheet ; these surfaces of marine denudation are dinted and pitted, like the rolled stones which rest upon them, with which the sea pelts the rock when a gale is on. I have taken rubbings from many surfaces of this kind, and they are alike everywhere. Close to the undermined rocks are rocks which have been undermined so as to break and fall ; and their angular fragments are rolling in the waves, to be made into pebbles for doing more work of the same land.

Near the place are caves, some hardly begun, others bored into the rock far beyond daylight, with waves at work in them. On the calmest days they make a wild hoarse rattle and murmur as they mine the rock with its own ruins. I could see no faults to account for these grooves, cliffs, and caves.

Here, then, are two different sets of tool-marks on opposite sides of a hill, both telling the same story of the destruction of rock to the depth of at least 2000 feet by ice and the sea.

But this sea-cliff is a geological section 2000 feet high, and several miles long, crossing the strike in a curved sweep. A glance at it after looking at the surface inland demonstrates, better than a volume could, that the structure of the rocks of which these mountains are made has little to do with shapes common in Irish and other hills. The vertical fracture breaks through the edges of contorted quartz beds, which are seen meandering and curving in great arches, folds, and bends, right up to the verge of the cliffs and the scarped hill-top. Not one of these well-marked curves corresponds in any degree to the edge of the upper surface. The plane floor cut horizontally by the edge of the sea below cuts shear through all curves