290 THE OCEAN, 



ward the south pole. So likewise we speak of the Indian Ocean as 

 extending from the eastern shores of Africa along the southern 

 coasts of Asia ; and the Atlantic Ocean as dividing Europe and 

 Africa from the two American continents, while the waters which 

 occupy the polar regions are catted the Northern Sea. 



Among the chief of those less expansive sheets of water, or those 

 properly called seas, we may mention the Baltic, the Mediterra- 

 nean Sea, the Black and the Red Seas : the Caspian Sea, being en- 

 tirely encorapassed by land, might properly be .styled a lake, but 

 as its water possesses the quality of saltness, it is ranked among the 

 seas ; yet Lake Superior, in North America, is supposed to be of 

 greater circumference than the Caspian Sea 3 the one being at least 

 fourteen hundred miles around its shores, and the other not more 

 than twelve hundred. 



Of the origin of this division into different seas, and seas of dif- 

 ferent depths, we cannot speak with certainty. It is highly proba- 

 ble that many of the larger excavations and partitions which we 

 meet wilh now, have existed, without much change in regard to 

 their extent, from the creation : others have undoubtedly been the 

 result of that conflict which is perpetually taking place between the 

 elements of land and water, and which has given rise for the most 

 part to islands, isthmuses and peninsulas : while subterraneous 

 Tolcanos, and the indefatigable exertions of corals, madrepores, 

 tubifores, and other restless and multitudinous zoophytes, 'hav 

 laid, and are daily laying a foundation for new islands or conti- 

 nents in the middle of the widest and deepest seas ; all which will 

 furnish us with an additional source of enquiry, and is indeed well 

 worthy of examination. 



There is another peculiar feature which characterises the waters 

 of the ocean, and which ought by no means to be overlooked on 

 the present occasion, and that is its tides and currents, and the 

 causes which have been assigned for them ; which will necessarily 

 lead us into an examination of the temperature of the ocean at dif- 

 ferent depths, the influence of the heavenly bodies, and especially 

 of the moon upon its general mass. 



The sections that follow under this chapter will be found directed 

 to these subjects, and will close that important and extensive 

 divisions of NATURAL HISTORY, which embraces the superficial 

 phenomena to which we have given the name of the globe. 



DITOR. 



