ABSTRACTS OF PAPERS 67 



seat of tectonic disturbances, wliicli were followed by the present cycle of 

 erosion. 



Presented by the senior author without manuscript. 



SOME CONCLUSIONS IN REGARD TO THE ORIGIN OF GYPSUM 

 BY FRANK A. WILDER 



(Abstract) 



While the salt-pan theory for the origin of gypsum has been generally ac- 

 cepted, its difficulties have been generally recognized and have often been 

 pointed out. While admitting that this theory best explains some gypsum de- 

 posits, it seems probable that many important bodies of gypsum owe their 

 origin to other causes and conditions. 



Professor Stieglitz has demonstrated that gypsum deposits that are free 

 from calcium carbonate can not be accounted for by the salt-pan theory. 

 Gypsum deposits of relatively recent origin of the salt-pan type are less impor- 

 tant than those having different origin. Present-day gypsum deposits are, for 

 the most part, efflorescent deposits, periodic lake deposits, spring deposits, and 

 deposits due to the alteration of carbonate to sulphate. There is reason to 

 believe that many important gypsum deposits of earlier periods owe their 

 origin to similar causes. 



Presented without notes. 



Discussion 



Prof. J. VoLNEY Lewis : Surface efflorescence is quite general over the out- 

 crop of gypsiferous Jurassic strata in Wyoming and Utah. Commonly this 

 takes the form of spongy crusts, but in places along the stream channels pow- 

 dery and granular gypsite, quite comparable to the Alamorgorda sands in 

 character, but very limited in quantity, has accumulated. Concentration by 

 ground water is also responsible for gypsum veins in many places, and the 

 question has arisen in my mind whether even some of the purer intercalated 

 gypsum beds themselves may not have originated in the same way. 



FLOODING OF OIL WELLS BY FRESH WATER 

 BY THOMAS C. BROWN 



(Abstract) 



It is well known that oil wells are frequently flooded by fresh water, coming 

 either from the surface or from porous strata penetrated by the well. The 

 older view was that the hydrostatic pressure of the water entering from above 

 forced the oil back into the rocks, or perhaps forced it off to some other outlet. 

 This theory will not explain the failure of many oil wells caused by the en- 

 trance of fresh water. 



In many of these wells the oil when pumped out is mixed with salt water, 

 and yet if fresh water enters in any considerable quantity the oil ceases to 

 come and only water can be pumped out. 



