388 r. A. AVILDER THE ORIGIN OF GYPSUM 



As a result of Stieglitz' work, it seems necessary to draw the conclusion 

 that it is very unlikely that gypsum that contains less than one-half of 1 

 per cent of calcium carbonate was formed under salt-pan conditions. 



Inasmuch as there are many published analyses of gypsum which con- 

 tain less than one-half of 1 per cent of calcium carbonate, it seems neces- 

 sary to take such deposits out of the salt-pan class or else to suspect that 

 the analyses were not made with sufficient care with reference to calcium 

 carbonate. In some cases there is ground for doubting the accuracy of 

 the analyses. Eecent analyses of the Fort Dodge, Iowa, gypsum, for in- 

 stance, show sufficient calcium carbonate to permit the supposition that 

 they were deposited from sea-water, though earlier analyses had shown 

 no carbonate. Analyses of a great many interesting and important de- 

 posits remain, however, that record no lime carbonate, and unquestionably 

 some of these analyses were carefully made and correctly represent the 

 composition of the deposit. This list of carbonate-free dejDosits contains 

 those in — 



Montana : Montana : 



Douglas, Great Falls, 



Empire Mountain. Armington, 



California : Boulder. 



Amboy, New Mexico : 



Palmdale. White Sands of Alamogordo. 



Florida : Oklahoma : 



Penasoffkee. Cement, 



Iowa : Medicine Lodge, 



Centerville. Southard. 



Kansas : Utah : 



Kling. Lovan, 



Nephi. 

 Wyoming: 



Red Buttes. 



Certain portions of the gypsum in Virginia and at Medicine Lodge, 

 Kansas, contain lime and magnesium carbonate, while other portions 

 seem to contain no carbonate. 



From the study of published descriptions of gypsum beds, it is appar- 

 ent that in most instances these beds rest directly on shale or sandstone. 

 This seems rather remarkable, in view of the amount of calcium carbonate 

 in ocean water and in the waters of rivers in arid regions. Some of this 

 carbonate may have been segregated near the entrance of the receiving 

 basin. Agencies that result in such segregation have been pointed out by 

 numerous observers. Nevertheless, it is not clear what becomes of much 

 of the carbonate, over and above that which Stiegiitz has shown must 

 come down with the gypsum. 



