OF COMMON SALT. 



159 



an uninterrupted series of movements of the earth's 

 crust has resulted in the almost continuous extraction of 

 salt from the sea, by the cubic mile, and the restoration 

 of fresh water, in the proportion of 60 cubic miles of water 

 to one of salt. It follows that down to the Tertiary period 

 the sea has been diminishing in density. We may even 

 make a rough calculation of its loss. The careful researches 

 of M. Krummel show that the volume of the entire sea is 

 3,138,000 cubic miles. Judging by its chemical composi- 

 tion, at a moderate estimate, it would contain at the present 

 time over 50,000 cubic miles of salt. Say that the Mayo mine 

 represents only the one -hundredth part of the existing salt 

 deposit. This is putting the salt deposits at the very largest, 

 for the Mayo mines, from comparisons I have made, would 

 seem to be equal to much more than one-hundredth part of all 

 known, and unknown, salt formations. Thus we get 1,000 

 cubic miles as the outside measure of all existing rock salt 

 formation. From this it would appear that the sea has, after 

 all, only lost about 2 per cent, of the salt it originally held. 



The same reasoning applies to the movements of gypsum. 

 "We may be sure that it was extracted from the sea in a 

 like ratio, and that the total loss, up to date, is 2 per cent, 

 of the amount once held in solution. 



Now, this loss of 2 per cent, of the salt once held in the 

 sea (of 1,000 parts in 50,000) is almost inappreciable. The 

 English Channel, according to Schweitzer, contains over 2*70 

 parts per cent, of salt. If all the salt in all the rock salt for- 

 mations was restored again to the sea, the channel water would 

 contain less than 2*76 per cent, of salt, that is, its increase of 

 salinity would be represented by less than *06 per cent. 

 No one would be the wiser for it, not even the fishes. 



But there is reason to suppose, that, for some thousands of 

 years past — since the Tertiary period — rock salt has ceased to 

 form, and a recuperative process, as regards the salinity of 



