xxxviii INTEODUCTIOlSr. 



attaining to 3000 feet, ttougli in Mayo, "Waterford, and "Wexford 

 some points are to be found slightly exceeding 2600 feet, and 

 Slieve Donard in the Monmes reaches almost to 2800 feet. 



In their petrological character, the ntunerous Irish mountain 

 groups are sufficiently varied. Granite is abundant in the Dublin 

 and Wicklow mountains and in those of Down and Donegal ; sand- 

 stones occur in Kerry, Tipperary, the Slieve Bloom range and 

 elsewhere ; quartz rock is abundant in the Galway and Mayo 

 groups and in Donegal ; mica-slate is of frequent occurrence ; 

 large masses of elevated limestone are found in Clare, Sligo, and 

 Fermanagh, and basalt covers a wide area in Antrim and Deny. 

 Chalk is conspicuously absent, for though exposed in cliffs at some 

 points along the Antrim coast, it is always capped with basalt, and 

 cannot be said to have any true outcrop in Ireland. Limestone 

 prevails almost throughout the central plain, but is usually covered 

 by extensive peat bogs or by drift accumulations frequently disposed 

 in the characteristic form of eshers or gravel mounds and ridges. 

 The area occupied by peat-bogs is very large, and has been estimated 

 at 4400 square miles, or 13-5 per cent, of the total surface of the 

 island. Somewhat more than half of this bog-area is lowland. 

 Much of the remainder lies at elevations between 1000 and 2000 

 feet above sea-level. 



The area of the country under water, chiefly in the form of 

 lakes, is little short of 1000 square miles, or fuUy 3 per cent, of the 

 whole surface. Eare and usually insignificant in the east, the lakes 

 become frequent towards the centre, and well-nigh innumerable in 

 some parts of the west, as in Connemara, Clare, and "West Mayo. 

 A comparison of the four western counties, Kerry, Clare, Gralway, 

 and Mayo, with an equal area of the eastern counties shows the 

 water-surface of the western counties to be fuUy four times as 

 large as that of the eastern. In the north-east is the low-lying 

 and shallow Lough Neagh, with an area of 153 squai-e miles, the 

 largest fresh-water surface in the British Isles. Owing to the 

 comparatively small extent of the country and the peculiar 

 disposition of the mountain-groups, most of the numerous Irish 

 rivers have small basins and short courses. But there is one 

 notable exception in the Shannon. This fine river, the longest in 

 the British Isles, and, perhaps, the lai-gest in volume, has a roughly 

 north and south course of about 260 miles, and widens in its middle 

 and lower reaches into the imposing river-lakes known as Lough 

 Eee and Lough Derg. 



