Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/232

 216 IRELAND [GEOGRAPHY. with the light-coloured strata below. In some places, however, as at the Giant s Causeway, the Cretaceous rocks disappear, and the basalt slopes gradually to the sea, displaying a series of terraces formed of hexagonal pillars, and occasionally separated by bands of volcanic ash. Coast-Line. Along the present coast-line there are to be seen in several places traces of ancient sea margins, the most continuous being those on the northern and eastern coasts, especially in county Antrim. Of still more ancient sea margins there are evidences in the terraces at the base or on the flanks of the mountains. The present coast-line, especially on the west and south, is very much indented by bays and inlets, which Hull, in his Geology of Ireland, attributes in many cases to the chemical action of the sea-water on the limestone rocks. On the south coast they most commonly run in a northerly direction with a westerly inclination at the upper end, and on the west coast the direction of the larger inlets is easterly, although several of the smaller ones run north, south, and north-east. Their troughs have mostly been excavated in the synclinal folds of the rocks, which therefore frequently project far into the sea in the form of high and bold headlands. On the northern coast the inlets generally run in a southerly or south-westerly direction. Most of those on the east coast have by the accumulation of sand been either wholly or partly formed into lagoons; and on the south-east coast the sea has made considerable encroachments on the land. The principal inlets are on the east coast Belfast Lough, Strangford Lough, Carlingford Lough, Dundalk Bay, Dublin Bay, and Wexford Harbour ; on the south coast Waterford Harbour, Dungarvan Harbour, Youghal Bay, and Cork Harbour; on the south-west coast Roaring Water Bay, Dunmanus Bay, Bantry Bay, Kenmare Biver, and Dingle Bay ; on the west coast Tralee Bay, the mouth of the Shannon, Galway Bay, Clew Bay, Blacksod Bay, Killala Bay, Sligo Bay, and Donegal Bay ; and on the north coast Sheep Haven, Lough Swilly, and Lough Foyle. In all, Irel ind possesses fourteen harbours suitable for the largest ships, seventeen for frigates, and over thirty for coasters, besides an immense number suitable for fishing boats. The islands of Ireland are small in size, and are situated near the mainland, most of them being formed of rocks from which, according to Hull, the adjoining Carboniferous strata had been denuded by the action of the sea-water. They are most numerous on the west coast, especially opposite Galway, Mayo, and Donegal. Off the Donegal coast the largest is Neish Aran. Separated from the mainland of Mayo by a narrow isthmus is Achill, the largest island of Ireland, and in Clew Bay there are an immense number of islets all formed of drift. An archipelago of granite rocks off the coast of Galway is formed of continua tions of the mountains, and at the mouth of Galway Bay are the three islands of Aran, composed of Carboniferous Limestone. Among the picturesque stacks of rocks off the coast of Kerry the most notable are the Skellings. The largest islands opposite Cork are Dursey Island, Bear Island, and Clear Island, south of which is a picturesque rock called the Fastnet, on which there is a lighthouse. On the east coast the principal are Lambay Island, Innis- patrick, and Ireland s Eye off county Dublin, and Copeland Island at the mouth of Belfast Lough. On the northern coast the principal are Rathlin Island off Antrim, and Tory Island off Donegal. Rivers and Canals. Several of the rivers of Ireland, including the largest of them, have had their channels determined by a previous physical condition of the land surface, and must have been formed during a long period of denudation. Many of the valleys are dried-up river beds, and along various of the present river valleys traces of old river terraces may still be seen. In some cases the alterations of the courses by breaks and dislocations of the strata are of very recent occurrence. In the districts of Sligo and Fermanagh, as well as of Galway, Clare, Kerry, and Cork, the rivers and streams have frequently cut out sub terraneous passages through the limestone, in some cases altogether disappearing : and along their courses turloughs or blind lakes, and abrupt deep holes called slue/gas are frequently formed. Owing to the moistness of the climate and the lie of the surface of the country, Ireland is more intersected by large rivers than England or Scotland, and it is a remarkable circumstance that in several cases there are groups of rivers with closely contiguous sources, which, however, flow in widely different directions. The largest river is the Shannon, which lias its source in the Carboniferous mountains of Fermanagh and Leitrim, and flows southward through Lough Allen, Lough Ree, and Lough Dearg to Limerick, where it opens out into a wide estuary and takes a westerly course to the ocean. Up to Limerick, where it becomes tidal, it is navigable for large vessels, and for vessels of small tonnage it is navigable within 5 miles of Lough Allen. Its course above Lough Dearg is very sluggish, but from that lake to Limerick its descent is very rapid. Its total length is 240 miles, and it drains an area of 4544 square miles. The Suir, the Nore, and the Barrow, which have their sources not far from each other in the Slieve Bloom mountains, and unite at Waterford, drain together an area of 3400 square miles. The Suir is navigable for boats as far as to Clonmel, and the Nore to Innistioge. The Barrow, by means of a branch of the Grand Canal, forms a line of 120 miles of inland navigation between Dublin and Waterford. The other principal rivers, all of which are to some extent navigable, are debouching on the west coast the Erne, the Moy, and the Corrib ; on the south coast the Blackwater and the Lee ; on the east coast the Lagan, the Boyne, the Liffey, and the Slaney ; and on the north coast the Bann and the Foyle. The Grand Canal, which with its various branches has a length of 165 miles, connects Dublin with the Shannon at Shannon Harbour ; and the Royal Canal, with a length of 76 miles, connects Dublin with the Shannon at Cloondora. Lines of inland navigation, partly natural and partly arti ficial, connect Lough Neagh with Belfast, Newry, and Lough Erne, From the sea at Galway there is communication by Lough Mask and Lough Corrib to Lough Carra. Since the introduction of railways the passenger traffic on the canals has wholly ceased, but the goods traffic is still considerable. Lakes. Many lakes of considerable extent exist both in the mountainous and lowland districts of Ireland, and the number of small lakes is very great. Altogether the area covered by lakes amounts to 711 square miles, of which 287 are in Ulster, 305 in Connaught, 69 in Munster, and 50 in Leinster. Lough Neagh in Ulster is the largest inland lake in the United Kingdom, and has an area of 153 square miles, with a general depth of from 20 to 40 feet. Lough Erne in Fermanagh has a length of upwards of 40 miles, but a breadth of only 8 miles. Properly speaking, it consists of two lakes 5 miles apart and con nected by a river, the upper lake being 13 miles in length with an area of 9278 acres, and the lower 24 miles in length with an area of 28,000 acres. Both lakes are dotted with numerous islets, and the lower one is famed for its picturesque beauty. Lough Corrib and Lough Mask have respectively an area of 43,484 and 22,219 acres. The country to the west of Lough Corrib contains about 130 lakes, 25 of which are more than a mile in length. The lakes of Killarney in Kerry, which are three in number and closely adjoin each other, are situated in the midst of wild and picturesque mountain scenery. The area of the lower lake is 5001 acres, of the middle one SSO,