THE LIME CARBONATE PROBLEM 389 



E. B. Branson^ states that — 



"A 40-foot bed of gypsum, resulting from the evaporation of 57,000 feet of 

 normal sea-water, should have nearly 3 feet of limestone below it, if the evap- 

 oration all took place in a restricted basin ; but if the waters were widespread 

 in the beginning, about half of the limestone might be deposited over the wider 

 area, as more than half of the CaCOg precipitates when the volume of sea- 

 water is reduced about 50 per cent, and the limestone below the gypsum might 

 be less than 2 feet in thickness. The writer has not seen limestone immedi- 

 ately below the gypsum at any place in the Red Beds." 



The localities listed above as containing important gypsum deposits 

 free from lime were selected because it was felt that the analyses were 

 carefully made, and that the analysis represented the average of the 

 mineral body and not merely a selected sample. For this reason particu- 

 lar weight was given to analyses made by the chemists in the employ of 

 manufacturers of gypsum products, for it was felt that they had a special 

 reason in securing an "average analysis." In the future, when gypsum 

 is analyzed, let us hope that the presence or absence of even small quanti- 

 ties of lime carbonate may be fully demonstrated. 



Nature of present-day Deposits 

 concentration of disseminated gypsum 



More attention should be directed to the gypsite beds of the western 

 United States, to the wonderful "white sands" of Alamogordo, New Mex- 

 ico, and to similar gypsum deposits in Utah and Australia. These are 

 generally recognized as originally efflorescent deposits, formed on the sur- 

 face by the evaporation of water that has seeped through gypsiferous 

 strata, the gypsum grains so formed being later piled up by the winds. 

 Salt that may have come to the surface with the gypsum readily leaches 

 out. The statement has been made by advocates of the salt-pan theory 

 that such wind-blown deposits can not be pure ; yet the gypsum dunes of 

 New Mexico, Utah, and Australia are remarkably pure. Gypsum de- 

 posits showing cross-bedding, like those reported in Oklahoma by L. C. 

 Snider,^ may represent efflorescent wind-blown material. 



According to G. W. Stose,^ the gypsum deposits of Virginia were prob- 

 ably derived from calcareous-argillaceous sediments which originally con- 

 tained disseminated gypsum. This gypsum, he believes, was concentrated 

 by underground waters which circulated along the fault between the Car- 

 boniferous and Cambrian rocks. While I am not prepared to wholly 



» Bull. Geol. Soc. Am., vol. 26, no. 2, p. 235. 



^ Mineral industry, vol. xxiv, p. .371. 



«U. S. Geol. Survey Bulletin 530, 1913, pp. 232-255. 



