SALT AND THE AGE OF THE EARTH 561 



in salt than those Devonian seas which yielded the salt of the 

 Salt Range. 



And the general aspect of the marine faunas of the various 

 periods do not indicate any gradual increase in the saltness of 

 the seas. The general facies of the Cretaceous fauna, in its 

 foraminifera, sea urchins, corals, molluscs, etc., is so like that 

 of the present ocean that it seems to require a sea not less salt. 

 Had the original ocean been saltless, should we not have ex- 

 pected to find an increasing fresh-water aspect in the fauna as 

 we went back in time ? But there is even a suggestion that the 

 ocean has been growing less salt. Consider the Mollusca. 

 Brachiopods, cephalopods, pteropods — which are exclusively 

 marine — have diminished in comparison with the lameiiibranchs 

 and gasteropods — which are also fresh-water forms . 



And if, as Prof. Joly suggests, the rocks of the earth are 

 having their sodium contents washed out continually, the 

 newer formed deposits should have less than the older. 



Thus a river which is cutting its way through Triassic rocks 

 may be dealing with matter which has had its sodium subject 

 to a like action, say in Carboniferous times. The rivers of 

 to-day must be bringing down less sodium than those of the 

 past. Is this possibly why the salmon requires to go to the 

 sea ? The river having become too fresh for it, the salmon must 

 go for the necessary saltness to the ocean. The eel, also, may 

 have found it impossible to complete its life history in the 

 river's growing scarcity of salt. 



As regards the assumption that the original ocean was 

 saltless, there is a serious objection. When the lowering of the 

 temperature permitted the water to condense, and collect in 

 the ocean hollows, it would dissolve the salt over the whole area 

 of its bed. Thus from the very first it would have a not in- 

 considerable amount of salt. 



Perhaps the most interesting point about the salt estimate 

 of the age of the earth is, that it is rather of the order of Lord 

 Kelvin's modest suggestion than of the somewhat sensational 

 figures given by the radium method. But while Lord Kelvin's 

 period dated from the first consolidation of the earth, Prof. 

 Joly's, dating from the first condensation of water in the ocean, 

 would be a little later in beginning. 



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