GEOLOGICAL PAPERS. 87 



same place and then drained at the right time to deposit most of their 

 gypsum and little of their salt. It is true that the gypsum area con- 

 tains some salt, which is so soluble that it is difficult to imagine any 

 way other than evaporation in which it could have been laid down, 

 but the salt beds do not require the supposition of such a series of 

 concentrations on a vast scale. Sea- water contains seventeen times as 

 much sodium chloride as calcium sulphate, and the thickness of the 

 salt beds is almost insigniiicant in comparison with the gypsum. 



Taking all these things into consideration, it seems th.at a small 

 part of the gypsum closely associated with the salt may have been 

 deposited by evaporation, but there must have been some other source 

 for the massive rock gypsum. 



A saturated solution of calcium sulphate and a saturated solution 

 of sodium chloride do not give any precipitate when they are mixed ; 

 so the gypsum could not have been precipitated by the salt in the 

 ocean. 



Large amounts of limestone have been removed from the land east 

 of the gypsum beds. This erosion was going on in Permian times, 

 and the lime must have been redeposited somewhere. The most 

 natural place to look for it would be on the western coast or marginal 

 sea bottom of that time. It is possible that the whole of the Red Beds 

 underlying the gypsum was formed at or near the advancing shore 

 line. This would account for the ripple-marks and for the presence 

 of so much sand, either alone or mixed with clay and other material. 



One of the properties of sulphides, especially of the alkalies and 

 alkaline earths, is the readiness with which they take up oxygen and 

 form sulphates. Springs containing soluble sulphides are not very 

 common, but there is at least one in Indian Territory,^ and it is prob- 

 able that there are others in some parts of the plains. There may 

 have been more such springs in earlier times, or there may have been 

 sulphur gases in contact with some strata. The Permian age is sup- 

 posed to have been one of disturbance and crust movements, and 

 therefore there may have been more sulphides and sulphur gases in 

 the springs or in contact with the strata below the surface than there 

 are now. If any sulphide existed, either in springs or in the soil 

 which was being eroded, a part of it would have been oxidized to a 

 sulphate and carried away by streams along with the limestone and 

 other material. The limestone, whether in solution or not. would be 

 changed to a sulphate and deposited as a sediment of gypsum at the 

 seacoast. 



The gypsum would follow the general laws of sediments, and the 

 amount would depend on the amount of sulphides or sulphates and 



4. Sulphur Springs, Chickasaw Nation, I. T. 



