Over all the south and east of England the elevations are comparatively insignificant; broad, undulating, grassy uplands, called the South Downs and the Chiltern Hills, rarely attaining more than eight hundred feet of elevation, follow the chalk formation across Southern England as far as Beachy Head on the Channel and the Foreland Cliffs on the Strait of Dover. The limestone Cotswold Hills between these and the Welsh Highlands rise somewhat higher.
Almost all the lowlands of Great Britain lie to the east and south. Here we find the plain of the “New Forest” in Hampshire and the treeless Salisbury Plain, the broad open Valley of the Thames, the “Eastern Plain” of Essex, Suffolk, and Norfolk, extending with rounded shores towards the North Sea; the low “Fen District” behind the shallow estuary of “The Wash,” from which many tracts have been reclaimed; the long “Plain of York” beyond; the valleys of the Tees and Tweed, the latter including the cultivated “Merse,” the march or border land of Berwickshire; the Scottish “Lowlands” between the Central and Southern Highlands; the “Carse” or alluvial plain of Gowrie, north of the Tay; “Strathmore,” the broad valley which extends between the Grampians and their southern outliers; the plain of Cromarty and the level moors of eastern Caithness farthest north of all. The only extensive lowlands on the western side of the island are the “Vale of Severn,” the “Plain of Cheshire,” between the Pennine chain and the Welsh Highlands, the lowlands round the estuary of the Solway, those of Ayrshire, and the Valley of the Clyde.
Crossing over to Ireland, though we find the lines of elevation running generally in the same direction as those of Great Britain, or from northeast to southwest, as shown in the peninsulas of the southwest coast, the mountains appear rather in detached clusters than in definite ranges, with shapes rather rounded than abrupt, forming a fringe round the coasts. The plateau of Antrim, which forms the precipice of Fair Head, the nearest point to the Scottish coast, contains the remarkable basaltic scenery of the Giants’ Causeway.
Giants’ Causeway.—This extensive and extraordinary assemblage of basaltic columns is in the county of Antrim, between Bengore Head and Port Rush. The name is sometimes given to the whole range of basalt cliffs along the coast, some of which reach the height of four or five hundred feet; but it is more properly restricted to a small portion of it where a platform of closely-ranged basalt columns from fifteen to thirty-six feet in height runs down into the sea in three divisions, known as the Little, the Middle, and the Grand Causeway. The last is from twenty to thirty feet wide, and stretches some nine hundred feet into the sea.
The Giants’ Causeway derives its name from the legend that it was built by giants as a road which was to stretch across the sea to Scotland. There are similar formations on the west coast of Scotland, on the island of Staffa.
In the southwest are the Mountains of Kerry, containing Cam Tual, the summit of all Ireland. The only important groups that lie centrally in the island are the mountains of western Tipperary.
Within the circle of these heights, and branching out between them at many points to the sea-coast, lies the Great Plain of Ireland, averaging perhaps two hundred feet in elevation above the sea. The highest point between Dublin and Galway, east to west across its center, is only three hundred and twenty feet above the sea-level. Many parts of it, such as that which surrounds Lough Neagh in the north, are scarcely fifty feet in elevation.
Rivers.—England and Ireland are very bountifully watered; Scotland rather less so, as the higher mountains of Great Britain rise in the west of the island, so the water-parting line following the greatest general height lies nearer the west than the east. The longer and gentler slope of the island is to the North Sea; the shorter and steeper to the Atlantic side. Hence most of the larger rivers belong to the North Sea drainage.
The Thames (Temz), the most important river of Great Britain, flows southeast by east across the southern portion of the country. It rises in the Cotswold Hills and follows a course of some one hundred and ninety miles to Gravesend, the head of the estuary, where it has a width of half a mile, gradually increasing then to ten miles at the Nore lightship about thirty miles farther. By the addition of its tributaries the Colne, Leach, and Churn, it becomes navigable for barge traffic at Lechlade, where the canal to the Severn leaves. Above Oxford the stream is frequently called the Isis. At Oxford the navigability improves, and river steamers ply between Oxford and points below it as far as London. Until the Tower Bridge, in London, was built, London Bridge was the lowest in the course, and ocean-going vessels still reach the latter.
Gravesend, twenty miles lower, grew up at the spot where vessels waited the turn of the tide; a little farther the Medway, by virtue of its estuary the most important tributary, enters; just inside this is Chatham, an important naval depot. Opposite Gravesend and on the north bank is Tilbury, the terminus of modern liners. The waters from the Tilbury docks to the Nore lightship are of great strategic importance, hence there is here a station for destroyers, torpedo-boats, and gun-boats. Sheerness and Shoreham as land defenses add to this.