14 HALF AN HOUR WITH THE WAVES. 



tance to its animal life, especially when we re- 

 member the great depths which prevail in some 

 parts of the sea. Formerly it was roughly estimated 

 that the greatest depth of the ocean would be some- 

 where about that of the greatest height of our 

 mountain chains. Some parts of the Pacific Ocean 

 have been sounded, and no bottom felt at more 

 than five miles. The Atlantic soundings for the 

 cable showed that in many parts the depth was 

 between two and three miles. It is now estimated 

 that the average depth of the sea below, is more than 

 fifteen times greater than the average height of the 

 land above the sea-level. The seas and oceans of 

 the globe occupy an area nearly three times greater 

 than the land, having about one hundred and forty- 

 eight millions of square miles of extent. To keep 

 up the density of this mighty body, we have seen 

 that a few currents, produced by the simplest causes, 

 are more or less sufficient. Sea-water is known to 

 contain nearly all the soluble salts and substances 

 existing on the globe. This led a French geologist 

 to hold that the present constituents of sea-water 

 date from the earliest period of our globe's history. 

 He says : " In the first stage of our planet, before 

 the watery vapours contained in the primitive 

 atmosphere were condensed, and before they had 

 begun to fall on the earth in the form of boiling 

 rain, the shell of the earth contained an infinite 

 variety of heterogeneous mineral substances, some 

 soluble in water, others not. When rain fell on the 



