198 The Realm of Nature CHAP. 



the continent itself rises. The breadth of the continental 

 shelf varies greatly. In the map (Plate XI.) the area of the 

 shelf is left white, and it will be seen to attain its maximum 

 breadth off Western Europe where the British Islands stand 

 upon it, off south-eastern America where it bears the Falk- 

 land Islands, around Florida, at intervals along the east 

 coast of Asia, and off the north of Australia. Along the 

 east and west coasts of Africa, and along the west coast of 

 America, it is very narrow, and around some volcanic islands 

 it is entirely absent. The total area of the continental 

 shelf, covered with water less than 100 fathoms deep, is 

 10,000,000 square miles. This includes the whole of 

 many shallow seas, such as the North Sea, the Baltic, the 

 White Sea, Hudson Bay, and the Yellow Sea, and unites 

 all the great continental islands, except Madagascar, 

 Celebes, and New Zealand, to their nearest continent. The 

 land bordering the coast-line is in most places a low un- 

 dulating plain, which rises gradually inland until it attains 

 an elevation of about 600 feet above the sea, and then rises 

 more abruptly to much greater heights. The low plains 

 (under 600 feet in elevation) measure altogether about 

 12,000,000 square miles. From the margin of the con- 

 tinental shelf to the end of the low plains there is therefore 

 an expanse of 22,000,000 square miles, the level of which 

 differs by only 1200 feet. Except possibly on the floor of 

 the Abysmal Area there is no other part of the Earth's 

 surface where so wide an expanse possesses such a 

 slight range of elevation ; and it is significant that 

 the coast-line at present almost bisects it, occupying the 

 only position in which a rise of 600 feet would submerge, 

 and a fall of 600 feet would enable it to lay bare so large 

 an area.-^tr 



265. Beach Formation. The upper margin of the 

 Transitional Area is a region of great activity and rapid 

 change. Tide and wind together urge the water against 

 the land and withdraw it, dragging back the solid material 

 it has seized. If the land is a low plain of very gentle 

 slope the waves gradually encroach upon it, drawing the 

 sand or soil seaward at every tide and building up the 



