52 THE BOTTOM Oh TUE SEA. 



and the salt water together, and the accidental 

 anomaly is soon lost to observation. 



Fresh-water is contributed even by the bottom of 

 the sea itself. It is true the phenomenon of sub- 

 marine springs is of rare occurrence, yet some re- 

 markable instances are known, and many others 

 may have escaped notice. In some places, generally 

 near the shore, the sea may be seen to bubble, and 

 yet no gas is disengaged. The movement is occa- 

 sionally so pronounced that the surface of the sea 

 swells as with a wave ; and if, in such a case, we test 

 the water, it will be found to be less salt than usual. 

 If the sample be taken from near the bottom, it will 

 prove to be nearly fresh ; indeed, if the source be 

 abundant, it will be found to be quite fresh. The 

 effect of these springs, however, is not traceable to 

 any considerable distance, and as they are always 

 near the shore, we can only regard them, in con- 

 nection with our subject, as objects of curiosity. 



3. Variations observed in the Gases contained in Sea-water. 



Sea-water not only contains salts, but gases. Air 

 penetrates into the sea, as water penetrates into the 

 atmosphere, in the state of vapour. Thus a kind of 

 exchange or reciprocity of action is established, and in 

 both cases a sort of refinement or purification is effected 



