770 



HISTORY OF THE SEA. 



a beef bone, thrown overboard by a sailor on a ship, may 

 form the nucleus of a new continent. The entire chalk clifls 

 of England were formed from the minute shells deposited by 

 the small animals which secreted them. At their death these 

 fell to the bottom, and thus slowly through the ages the de- 

 posit was formed. The recent deep sea dredgings have shown 

 the sea, at all depths, is full of animal life ; and as the steady 

 fall of snow-flakes in a winter's storm, piled up by currents 

 of wind, form the drifts, or falling quietly, cover the ground 

 uniformly, so the sea is full of the minute shells, which, car- 

 ried by currents, form banks, or, falling evenly, prepare the 

 plains which in the future will appear, in some upheaval, to 

 form new continents. 



In the United States the peninsula of Florida is an evidence 

 of the land produced by the labor of the coral polyp. Florida 

 has now ceased to increase toward the east, for on this side it 

 touches the deep waters of the gulf, and the polyps can live 

 only in shallow water. The peninsula increases only on its 

 southern and western coasts. The cut at the end of this 

 chapter represents the appearance of coral islands as they 

 first rise to the surface, before the gathering soil provides the 

 conditions for covering them with the luxuriant vegetation of 

 the tropics. 



The cut at the head of this chapter, of an aquarium, repre- 

 sents a new appliance of modern times, which is a most valu- 

 able aid in our obtaining a knowledge of the habits of the 

 animals living in the sea. In fresh water, as well as in salt, 

 the mutual relations of the vegetable and animal life serve to 

 keep the water from becoming stagnant. The plants secrete 

 the carbonic acid gas, which the animals give to the water by 

 breathing, and in so doing free the oxygen which the animals 

 reauire. In keeping therefore an aquarium, the desired point 

 is to provide such a natural proportion of vegetable and animaj 

 life as shall preserve this balance. In many of the larger 



