210 MOTION OF THE SEA. 



the first that addresses our understanding, is the vast 

 extent of its usefulness. The evaporation of water from 

 its surface, cleared from the impurities of the land, and 

 adapted for the promoting of life and fertility, has already 

 been mentioned. But the ocean is also the grand mes- 

 senger of physical nature : that general law, or pheno- 

 menon of the constitution of matter, (for the laws and the 

 phenomena of nature are the same,) by which the earth 

 is maintained in its orbit, and has the figure and con- 

 sistency which it possesses, and by which the objects 

 on its surface preserve their forms and their places, 

 that simple law occasions the tides of the ocean ; and 

 these, by moving in the very directions which an obedi- 

 ence to this law points out, produce currents, by means 

 of which there is a constant circulation of the waters of 

 the ocean through all parts of the earth's surface ; and 

 the immediate consequence is an equalization of warmth, 

 by means of which, the extremes, both of heat and cold, 

 are mitigated, and the general fertility and comfort 

 promoted. 



But, when we come to look a little more attentively 

 at the structure of the earth, we find that the ocean has 

 been one of the grand agents in elaborating it to its pre- 

 sent consistency. Large tracks are covered, to a great 

 depth, by beds of gravel, containing nodules of the hard- 

 est stone, which are not in angular masses, as if they 

 had been reduced from their native rocks by any action 

 apart from the water such as that which, by means 

 of alternate frost and thaw, produces the heaps of 

 broken stone that we find on the brows of rocky moun- 

 tains, and at the bottoms of precipices but smoothed, 

 and rounded, as if they had been for ages rolled upon 



