HYDROGRAPHY. There is no well-defined water parting feature in the country with rivers radiat ing from it. There is, therefore, DO reason why a stream rising in one of the central counties should flow to the Irish Sea rather than to the Atlantic Ocean. The central plain, in fact. is a gathering ground for the waters that flow down the inner slopes of the bordering hills, and for the rock waste that they carry with them. Most of the plain is not over 500 feet above sea-level. The water parting between the eastern and western rivers may be traced from Lough Foyle to Mizen Head; but it is a winding line, marked by no definite and determining surface features.
The rainfall is abundant in the central plain. with the result that the slow-moving rivers widen into long lakes or loughs. The Shannon and Erne rivers are formed by these lakes, joined by stretches of river, the river sections being not very much longer than the The northern part of the central plain is drained by the Erne. The centre of the plain is drained by the Shannon. which empties:, into the Atlantic through a wide estuary 70 miles in length. The
Shannon. 250 miles long, is the longest river in the United Kingdom. Nearly half of it above the estuary is made up of the three lakes Allen. Rec. and Derg. All the most important rivers rise on the plain, the mountain streams being too limited in length and drainage area to have large volumes. Some of the plain streams, like the Boyne. are true rivers, and not made up partly of lakes. A few of these sluggish rivers serve as means of communication with the interior, and their usefulness is augmented by the con siderably developed canal system of the country. The Shannon River, navigable by large steamers for 129 miles. is connected with Dublin by the Grand and Royal canals, thus affording water communication across the island. Bogs covering a large part of the plain are the source of peat, so extensively used in Ireland for fuel. The Bog of Allen. to the east of the centre of the plain, is the most extensive of these wet, barren legions.