Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/257

 a general N.E. and N.W. extension, and cross meridians from 6° to 10° west, diagonally between latitudes 51° and 56° north. There must be some reason for the shape of the coast and surface of this part of the earth's solid crust.

III. Under Water. — Beyond high-water mark in harbours the sea now packs layers of mud and shingle in rocky hollows ; but near the coast, and far out at sea, peaks of rock stand up in the midst of undulating plains of drift, of which the charts give the form in fathoms below the plane of the water. The limit of 600 feet is far from shore. The sea-bottom about Ireland is an undulating plain with rocky hills in it, very like plains on shore.

IV. On Shore. — The greater part of the area of Ireland consists of low undulating rock-surfaces, covered with Boulder-clay, with water drifts of sand and gravel, with soil and peat-bogs. Amidst this cover of loose materials stand groups of bare rocky mountains, and isolated hills, knolls, and hillocks of solid rock. The highest point in Ireland is 3404 feet above the sea-level, near Killarney, in the S.W. So far as my own observations and my reading enable me to form an opinion, the present shape of all the rock-surfaces in Ireland, from the highest tops to the sea-level, is the result of wearing and waste ; and the shape of the low lands is the result of packing fragments, broken, crushed, ground, or worn off solid rocks. Some great denuding engines must have worked on this region.

As the drift is commonly " glacial " next to the rock, and as most of the rock-surfaces in Ireland still are " glaciated " where they have been protected from water and weather, I attribute the present shape of the surface of Ireland chiefly to glacial action during a geological period later than the formation of the Antrim chalk.

V. Denudation*. — That large masses of solid rock have been

to lend me a map marked with the broad arrow of the Ordnance Survey, and thus described on the face of it : —
 * On the day before this paper was read, Professor Ramsay was kind enough

" Map of Ireland to accompany the report of the Railway Commissioners, 1838, &c, &c. ; engraved under the direction of Lieut. Larcom, Royal Engineers, May 1837 (in MS.). Coloured to represent portions of Ireland which would be above water if it was depressed 500 feet, and to show the positions of the escars and gravel deposits with reference to the islands which would be formed. Signed Henry James, Capt. Royal Engineers."

This map was placed beside a geological map of Ireland to show that elevations and depressions do not coincide with local geological disturbances, but with " surface denudations." The map, coloured black on a blue ground, shows two groups of more than 450 small islands. Their shape is irregular ; but long narrow points trend south-westward; blunt ends are generally towards the north-east, and cliffs face the Atlantic and the north-west. Beside these maps were placed a travelling map, with notes of observations made in Ireland, and shaded Ordnance maps of Scotland, with thick ice, drawn to scale. Coast-lines of the supposed Irish archipelago correspond to many inland cliffs. " Drumlins," escars, osar, kames (Gaelic "ceum," a foot-path), and ridges of drift described by Messrs. Close & Kinahan, mentioned in this paper, shown on shaded Ordnance maps, and conspicuous in all glaciated countries known to me, are shown here to correspond in direction to the probable run of tides in sounds and wide passages less than 500 feet deep. These now are passes, hollows, lowlands, undulating plains of sands and gravel, bogs and large lakes, in Ireland ; the islands now are isolated rocks with the shape of " Crag and tail," and