958 A TREATISE ON METAMORPHISM. 



Clarke's average for the original rocks is- 0.1 748. It thus appears as if 

 there were an excess of sulphur in the secondary rocks amounting to 0.2847 

 per cent. To this excess, upon the theory that the salts of the ocean have 

 been derived from the original rocks, should be added the vast amount of 

 S0 3 in the ocean. Reckoned as sulphur, from Dittmar's estimates this is 

 1,187,000,000,000,000 metric tons, which corresponds to 2,964,000,000,- 

 000,000 metric tons of S0 3 . But this is only .439 per cent of the total mass 

 of the sediments. 



The above calculations as to the amount of S0 3 in the sediments take 

 no account of gypsum deposits. If these be supposed to contain one-tenth 

 as much S0 3 as the ocean, namely, .0439 per cent of the total amount of 

 sediments, there is in the sediments and the ocean together an excess of 

 .7676 per cent beyond the amount calculated in the original rocks. 



These facts show that there is a great discrepancy between Clarke's 

 estimate of 0.1748 per cent of S0 3 in the original igneous rocks and the 

 amount of sulphur in the secondary rocks. It is thought highly probable 

 that this discrepancy is largely explained by the actual escape of much 

 sulphur as a gas during periods of volcanism, as hydrogen sulphide, which 

 is oxidized during volcanic action, or by the direct oxidation of the sulphur 

 to S0 2 or S0 3 . It is certain that the amount of sulphur may be greater in 

 the secondary than in the original rocks, as is shown by analyses, because 

 the original rocks contain only the residual sulphur which separated as a 

 sulphide when the magma crystallized. While the igneous rocks may lose 

 a considerable portion of their sulphur before crystallization, this may not 

 fully explain the discrepancy. It is possible of course that Clarke's estimate 

 of sulphur in the original ig*neous rocks may be somewhat too small, since 

 this element is in such subordinate amount, and selections for analysis were 

 made upon the basis of other elements rather than to get an average sample 

 for sulphur. 



As to the geological processes through which the redistribution of the 

 sulphur takes place, the following summary statement may be made: In the 

 alteration of the original rocks in the belt of weathering, the sulphides are 

 largely oxidized to sulphates, which are for the most part taken into solution 

 by the underground waters. Some of this dissolved material is carried 

 down into the belt of cementation, and a portion is there precipitated as 

 sulphate in the form of barite, celestite, and gypsum; another part is again 



