SULPHUR IN ORIGINAL AND SECONDARY ROCKS. 957 



SULPHUR. 



According to Clarke's estimate of 1891 sulphur forms 0.04 per cent of 

 the outer 10 miles (16.1 kilometers) of the earth, including the original rocks, 

 hydrosphere, and atmosphere, 0.09 per cent of the ocean, and 0.03 per cent 

 of the original rocks. However, in his estimate of 1900 the amount in the 

 original rocks is increased to 0.07 per cent. Sulphur thus has fourteenth 

 place in the scale of abundance." If the sulphur were reckoned as con- 

 tained in S0 3 Clarke's estimates for 1891 and 1900 for the original rocks 

 would be 0.0749 and 0.1748, respectively. 



It is well known that sulphides are constituents of the original igneous 

 rocks. Sulphur occurs in these rocks as pyrite and pyrrhotite certainly. 

 Sulphur is found also in the meteorites in the form of troilite (FeS), possibly 

 as pyrrhotite (Fe n S n+1 ), as oldhamite (CaS 3 ), and also in the hydrocarbon 

 (C 4 H 12 S 5 ). It thus appears that there are various sources of sulphur in the 

 material of which the earth is formed. 



Sulphur occurs in the shales, sandstones, and limestones as sulphates 

 and sulphides. The amount of S0 3 reported by Clarke in 78 shales is 0.65 

 per cent ; in 624 sandstones, 0.08 per cent. No sulphur as sulphide is 

 reported, but Clarke writes that the above determinations include probably 

 both the sulphur as sulphate and as sulphide. The amount of S0 3 in 843 

 limestones is 0.06 per cent, and the amount of sulphur as sulphides in these 

 limestones is 0.08. The latter amount corresponds to 0.20 per cent S0 3 , 

 and thus if all of the sulphur of the limestones were reckoned as S0 3 the 

 amount would be 0.26 per cent. 



It thus appears that, taking into account the molecular weights of 

 sulphur and S0 3 , sulphur is about four times as abundant in the shales as 

 in the original rocks, is reduced by about one-half in the sandstones, and 

 is increased by about one-half in the limestones. Since the volume of the 

 shales is so great, the amount of S0 3 in the shales is much more than suffi- 

 cient to compensate for the deficiency in the sandstones even if the excess 

 in the limestones were ignored. If one were to combine amounts of sedi- 

 ments and percentage of S0 3 in these rocks, and thus make an estimate of 

 the amount of the compound there should be in the original rocks, he would 

 have the following equation: 



.65X.65 + .08X.30+.26X.05=.4595 



« Clarke, cit., Bull. 78, p. 39; Bull. 168, p. 15. 



