ABSTRACTS OF PAPERS 103 



dailj'. As yet there is no proof of any geological structure to cause tlie accu- 

 mulation, which seems to be in a very limited area. The close spacing of the 

 drill holes, which often does not exceed 100 feet, will probably result in a 

 rapid exhaustion of the supply. 



Read in full from manuscript. 



Remarks were made by Messrs. W. Lindgi-en and R. S. Woodward, 

 and reply by the author. 



ORIGIN OF THICK SALT AND QYP8UM DEPOSITS 

 BY E. B. BRANSON 



{Abstract) 



The main difficulties in explaining the origin of thick salt and gypsum de- 

 posits which are not in association are: (1) in accounting for basins deep 

 enough to hold the necessary volume of water; (2) in explaining the rarity 

 of other salts in the deposits; (3) in accounting for the absence of salt de- 

 posits above the gypsum ; (4) in explaining the absence of sedimentary im- 

 purities, and (5) in accounting for the absence of fossils. These difficulties 

 are met by a modified bar hypothesis, which assumes that on the drying up 

 of large interior seas the waters became isolated into smaller basins, with 

 marginal basins overflowing on account of receiving the drainage formerly 

 coming into the larger seas, and that in the overflow concentrated waters were 

 brought to the innermost isolated basins, and evaporation from these caused 

 riipid deposition of salt or gypsum. The absence of interbedding of salt and 

 gypsum may be due to the gjpsum having been precipitated out before the 

 highly concentrated waters entered the innermost basins. 



Read in full from manuscript. 



Discussion 



Prof. L. V. PiRssoN desired to point out that if he understood the purpose 

 of the paper, it seemed to him that the matter of the lateral circulation of 

 saline solutions of differing concentration and density had not been sufficiently 

 discussed. If there were a primary basin of concentration which brought the 

 sea-water to one-fifth the original volume, when fresh water from the drainage 

 basin came in on this it would, from its lower density, float on the heavier 

 solution and rise to the basin rim. An example of this is seen in the Amazon, 

 whose fresh water floats over the sea-water to a great distance out in the 

 ocean when the overflow from the first basin took place. If this is due to 

 seasonal precipitation, it would be liugely of fresh water carrying some of the 

 denser solution with it, especially toward the end of the overflow; or, in other 

 words, it is hard to see how the dense solution could be inovcil out oi' its Itasin 

 into the .second one without mixing :nul coiisciiiUMit dilution. 



I'rofessor l'ir.s.son also pointed out that in a suitable arraiigfuient uf salt 

 lake, bar, and bay, where ev.iporation was greatest over the latter, it was 

 conceivable Hint tluTc miglit be .iii inward surface current into the bay. a 

 sinking of tlie concentrating saline w.itci-. ;nid an outward bottom current of 



