5-82 PROCEEDINGS OF THE ACADEMY OF [1888. 



enriched in saline matter and rise in temperature.^ The greater 

 part of the deliquescent magnesium salts however remains in the 

 upper layers, while chloride of sodium is found preponderating below. 

 As the saltness increases, organisms possessing free locomotive 

 power, are compelled to seek a new habitat and make their escape 

 Into the open sea against the currents and waves sweeping over the 

 bar ; those without free movement die off and generally leave only 

 indistinct remains in the strata, which are nest deposited. The 

 formation of the latter commences with the precipitation of oxide of 

 iron and carbonate of lime, as soon as the concentration has pro- 

 ceeded so far as to double the amount of saline matter in the lagoon 

 and then ceases until the solution contains five times as much salts, 

 when a second layer of carbonate of lime settles, this being brought 

 iibout by a double decomposition between the soda and gypsum held 

 in solution in producing calcium carbonate and sodium sulphate. 

 At the same time gypsum begins to deposit and constitutes the basis 

 proper. As soon as the saline solution has increased its weight of 

 salts eleven times, its specific gravity reaches r22 and the precipita- 

 tion of chloride of sodium begins in the form of the well know foliated 

 crystalline masses, accompanied by some calcium sulphate etc., added 

 from the sea-water running in. 



Though generally speaking the sediments follow in reverse order 

 of their solubilities, as Usiglio ^ has shown in his exhaustive experi- 

 ments, it often happens that small quantities of easily soluble salts 

 are mechanically included in the others; thus magnesium sulphate 

 is frequently found contaminating rock-salt, and especially there, 

 ■where clayey mud washed in, and was deposited at the same time. 

 Then again some substances, only scantily represented in sea-water, 

 remain longer in solution than we should be led to expect from labo- 



^ By this interchange of heat downwards the constant temperature of 14C°. to a 

 depth of 4000 meters in the Mediterranean can be accounted for, the high barrier 

 at the Straits of Gibraltar cutting this sea off from the Atlantic ; westwards of the 

 entrance to the Mediterranean on the other hand, we find extending to the same 

 depth, an icy temperature of 0° to 40°. Accordingly deep sea currents rich in 

 chloride of sodium flow from the Mediterranean into the Atlantic as well as the 

 Black Sea, and are compensated by return surface currents. As a result of this 

 circulation, the surface water of the Mediterranean is rich in magnesium salts, 

 whilst the Black Sea, analogous to the Baltic, does not contain ocean water diluted 

 %vith fresh-water as one might at first be led to expect from the great influx of river- 

 water, but shows a preponderating amount of sodium chloride. 



2 Ann. Chim. et Thys. 27, 172. 



