Skull of Whale, with the Baleen, 98 Sockets with teeth, of Echinus esculentus, 339 Surirella constricta, 402 Theoretic representation of the Circulation in Fishes, 192 Theoretic representation of the Circulation in Mammals and Birds, 175 Theoretic representation of the Circulation in Reptiles, 175 Torso Rock, near Point Deas Thomson, in the Arctic Ocean, 9 Urticating organs of Cœlenterata, 346 Water-Sports, 69, 70 PART I. THE PHYSICAL GEOGRAPHY OF THE SEA. [Illustration] CHAPTER I. THE MAGNITUDE OF THE SEA. Extent of the Ocean.--Length of its Coast-Line.--Mural, Rocky, and Flat Coasts.--How deep is the Sea?--Average Depth of the Atlantic Ocean.--The Telegraphic Plateau between Newfoundland and Ireland.--Measurement of Depth by the Rapidity of the Tide-Wave.--Progressive Changes in the Limits of the Ocean.--Alluvial Deposits.--Upheaving.--Subsidence.--Does the Level of the Sea remain unchanged, and is it everywhere the same?--Composition and Temperature of Sea-Water.--Its intrinsic Colour.--The Azure Grotto at Capri.--Modification of Colour owing to Animals and Plants.--Submarine Landscapes viewed through the Clear Waters. Of all the gods that divide the empire of the earth, Neptune rules over the widest realms. If a giant-hand were to uproot the Andes and cast them into the sea, they would be engulphed in the abyss, and scarcely raise the general level of the waters. The South American Pampas, bounded on the north by tropical palm-trees, and on the south by wintry firs, are no doubt of magnificent dimensions, yet these vast deserts seem insignificant when compared with the boundless plains of earth-encircling ocean. Nay! a whole continent, even America or Asia, appears small against the immensity of the sea, which covers with its rolling waves nearly three-fourths of the entire surface of the globe.