Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/233

 MINERALS.] IRELAND 21 and of the upper one 430, Lough Dearg, a small lake in the south of Donegal, has been resorted to from time immemorial as a place of penance by Roman Catholics. The other lake of the same name in the course of the Shannon has an area of 29,570 acres. The other principal lake districts are Sligo, Cavan, Westmeath, and Longford. Hull, in his Geology of Ireland, makes a classification of the lakes, according to their modes of formation, under the three heads of (1) lakes of mechanical origin, (2) lakes of glacial origin, and (3) lakes of chemical solution. Of the first group, which are those whose formation is due chiefly to faults or dislocation of the strata, he mentions as special examples Lough Neagh and Lough Allen, both of which originated before the Glacial period, and probably between the Miocene and Pliocene periods. Those of glacial origin occur in the mountainous districts, and are clue either to the scooping out of the rocks by the passage of ice over their surface, or to the accumulation of embank ments at the end of the valleys or hollows. Those due to chemical solution are situated either on the limestone plain or in districts where the limestone formation has penetrated, and have been produced by the solution of the limestone through the action of water containing carbonic acid gas. , Coed. Of the Upper Carboniferous beds which at one time overspread the central plain of Ireland, only small patches remain in isolated spots, serving chiefly as an indica tion of the immense loss that has been sustained in an important ebment of material prosperity. The principal coal-fields are the Leinster, the Munster, the Conriaught, and the Tyrone. The Lsinster or Castlecomer field, situated between the Nore and Barrow, consists of a range of hills varying from 800 to 1000 feet high, and extending over portions of Kilkenny, Queen s county, and Carlow. It lies in the form of a basin, its most productive beds occupying the centra. These are the Middle Measures, but in the field both the Middle and Lower are represented. The coal is anthracite. The most common fossils are either terrestrial or freshwater, marine fossils being found chiefly in some of the upper beds. Above the Barrow coal in county Kilkenny several remarkable reptilian remains have been found. The Lower Measures consist of gannister beds resting upon Carlow flags, and contain some beds of shale and a few thin seams of coal, with several beds of marine fossils. This field is the most important in Ireland, and yields a larger weight of coal than all the others together. The West Muuster coal-field occupies portions of Clare, Limerick, Kerry, and Cork, and consists of a series of low hills extending from near Galway Bay in the north to Killarney in the south. All the three measures are repre sented, but there are only a very few workable seams, as most of the coal is very thin, and the strata very much inverted. The principal collieries are at Dunhallow in Cork, and the coal, which is anthracite, is used chiefly for lime-burning. Many of the Lower Measures are very rich both in terrestrial and in marine fossils. The East Munster coal-field consists of a low range of hills in Tipperary, closely adjoining the Carboniferous hills in Leinster, from which they are separated by the river Nore. Thence it extends to near Cashel, a distance of about 20 miles, and its average breadth is about 5 miles. All the measures are represented. The productive portion of the field is at Killenaule, and consists of two thin seams in the Upper Measure. In the Lower Measures the principal fossils are marine ; and plant impressions, especi ally those of ferns, are very numerous. The Connaught coal-field embraces the mountainous district round Lough Allen, and includes portions of Sligo, Roscommon, and Leitrim in Connaught, and of Fermanagh and Cavan in Ulster. Both the Middle and Lower Measures are represented. They are composed chiefly of yellow sand stone and shale, and are overlaid by beds of grit. The coal is bituminous, and a large portion of it is workable. The Tyrone coal-field includes the district between Dungannon and Lough Neagh, having a length of 6 and a breadth of 1 to 2 miles, and the small basin of Annaghone a little to the north. All the measures are represented. The coals have been worked only near the surface, but it is believed that very extensive and valuable seams of workable coal exist at lower depths. The average quantity of coal raised in Ireland annually is about 130,000 tons, of which about 80,000 are raised in Leinster, 30,000 in Munster, 16,000 in Antrim and Tyrone, and 6000 in Leitrim and Roscommon. As the annual im portation of coal exceeds 2,000,000 tons, it is evident that the coal supply obtained from Ireland s own mines is quite a minor element in its prosperity ; but the industry might be much more largely developed, the total available amount of coal being estimated at 180,000,000 tons. Peat. For the absence of coal the country is to some extent compensated by the supply of peat fuel obtained from the red bogs situated in the central plain, and occupying a large tract included within two lines drawn across the island, the one from the Hill of Howth to Sligo, and the other from Wicklow to Galway. Originally this district was occupied by a forest, principally of oak trees, which after being gradually killed by the growth of mosses and other peat-producing plants, were succeeded by a forest of firs, these also in turn perishing. The average depth of the bog is 25 feet, but in some cases it is over 40 feet. According to its depth it varies in colour, from whitish brown to a brown-black closely resembling coal. The brown or red turf in the centre forms the best fuel. The lower strata sometimes pass into lignite. Lignite of an immense thickness is found around the southern shores of Lough Neagh. In the mountain districts the bogs usually consist of brown turf of only about 12 inches thickness. Preglacial or interglacial peat has been found in Queen s county, county Galway, and county Tipperary, and submarine bogs with remains of an ancient pine forest have been discovered off the south-west coast. The bogs of the central plain contain in a state of good preservation animal and human skeletons, tree canoes, gold and silver coins and ornaments, crannogs or lake dwellings, log houses, and wooden roadways. The total area occupied by bog is 2,830,000 acres, or about one- seventh of the surface of the island, mountain bog occupy ing 1,254,000 acres, and fiat red bog 1,576,000 acres. Iron. The deficiency in coal supply is the more to be regretted in the case of Ireland on account of its immense stores of iron, which for want of proper fuel remain unutilized. Red hematitic iron of a very rich kind is found associated with the coal-fields in the districts of Tyrone, and in Cork and Waterford. Valuable pisolitic ore occurs between the sheets of basalt in Antrim. Iron is met with in great quantities in the bogs, and is easily fusible, but the quality is not nearly so good as that of the clay iron which occurs in great abundance in the coal districts of Connaught. Some centuries ago the manufacture of iron was one of the most important industries of Ireland, the surface of the country being dotted over with small iron works, in which the ore was smelted by wood charcoal; but as the supply of wood became exhausted the industry was wholly discontinued, the last of the old furnaces having been put out more than a hundred years ago. On the discovery of coal at the Arigna river near Lough Allen,, iron-works were established there in 1788 which were carried on until 1808, and again revived in 1825, when the undertaking failed on account of the insufficiency of capital with which the company started. Of late years XIII. 28