66 NEW YORK STATE MUSEUM 



from the Mediterranean, which has a shghtly higher content of 

 soMid matter than the 0!pen ocean, but which does not differ notice- 

 ably in the relative proportions of the several ingredients. 



By evaporation of the water, which at the start had a density of 

 1. 02, no marked deposition took place until the specific gravity of 

 1.05 was reached, when the volume had been reduced to 53 per 

 cent of the oiriginal. Between this density and that of 1.13, the 

 iro-n oxid and calcium carbonate were precipitated. Then, with a 

 volume of only 19 per cent of the original, the solution began to 

 depoisit gypsum which continued to come down until the density 

 reached 1.26. At a density of 1.214, when only 9.5 per cent of the 

 solution remained, salt was depO'sited along with magnesium sulfate 

 and chlorid. Further concentration brought down the more soluble 

 salts in variable order, but sufficient details have been given for the 

 piresent purpO'se. 



The sequence of deposits from sea waters accordingly is first lime- 

 stone and ferric oxid, next gypsum, and then salt and magnesium 

 compounds. Gypsum is precipitated when 81 per cent of the water 

 is evaporated and salt when a little over 90 per cent is removed. 



The formation of gypsum beds in association with limestones and 

 salt deposits is thus a simple process. But the evaporation of a 

 relatively shallow lake or an arm of the sea alone would scarcely 

 afford any considerable thickness of gypsum. Of the total solid 

 matter in sea water, amounting to 3.5 parts in 100, only about 3.6 

 per cent consists of calcium sulfate. The extensive accumulations 

 of salt and gypsum are to be explained, probably, by some such 

 method as that advocated by Ochsenius. According to his theory 

 the deposition occurred in nearly inclosed arms of the sea or 

 lagoons. If a bay or lagoon is connected with the sea by a narrow 

 and shallow channel, evaporation will cause the denser brine formed 

 at the surface to sink and concentrate at the bottom while its dif- 

 fusion will be prevented by the shallow opening seaward. Surface 

 currents may enter from the sea, however, to maintain an equilib- 

 rium with evaporation. Provided there is little land drainage in 

 the bay, the salinity of the water will increase until saturated, and 

 deposition of the constituents will then occur in regular se- 

 quence. The process may be interrupted of course at any time by 

 an unusual influx of water, or there may be periodic fluctuations oi 

 supply so as to produce an alternating series of deposits. That 

 thi's method of concentration affords an explanation for many of 

 the salt and gypsum beds is made probable by the fact that there 

 are present day examples of its operation. Some of the bays on 



