REDISTRIBUTION OF CHLORINE. 979 



an amount of chlorine in the limestones somewhat greater than the average 

 for the original rocks is not easy to understand. The explanation may lie 

 in the fact that limestones are the home of the phosphates and that the 

 phosphate apatite is a chlorine-bearing- mineral. 



A large part of the chlorine which was present in the original igneous 

 rocks and which has escaped into the atmosphere through volcanoes has 

 passed into the hydrosphere. Under ordinary conditions, after the chlorine 

 is once taken into solution apparently very little of it is again redeposited. 

 It continues in the circulating waters until it reaches the sea, in which it 

 appears to have been segregating- during geological time. Of all the 

 elements of the salts of the sea it is by far the most abundant. According 

 to Dittmar's estimates it composes 55.292 per cent of the total salts, or 

 more than half of all the compounds held in solution in the sea. This 

 would amount to 25,557,000,000,000,000 metric tons. 



"While a large part of the chlorine which has been subjected to 

 metamorphic j>rocesses has been carried to the sea, at places where there 

 are inclosed basins, as for instance the Great Basin, the Dead Sea, etc, 

 chloride deposits have been built up. Locall}?' these are of considerable 

 magnitude. Moreover, during geological ages chloride deposits, mainly of 

 sodium, have accumulated in abundance, so that considerable beds con- 

 taining variable percentages of chlorine have been buried below later 

 sediments. Such material furnishes the rock salt of the salt mines, for 

 instance, of Poland, and the brines of many salt-producing districts, such 

 as those of New York and Michigan. 



As yet it is entirely impracticable to estimate the amount of chlorine 

 which is locked up in the rocks as sodium chloride. It has been the 

 common impression that the major portion of the sodium chloride is in the 

 sea rather than in such deposits. It is subsequently suggested that this 

 impression may be erroneous (see pp. 997-998), and that the great amount 

 of segregated sodium is in the salt deposits rather than in the sea. If this 

 be true for that element, it would also be true for chlorine. 



The chlorine concentrated with sodium in the salt deposits and the sea 

 is the great economic product resulting from the segregation of this element 

 in large proportions from material originally very sparsely disseminated. 

 The great importance of sodium-chloride to man and to animal life in 

 general is so well known that it need not be emphasized. 



