THE FORMATION OF SALINE MINERAL WATERS. 833 



second time, and new strata of gypsum will be precipitated upon the 

 marls containing the marine shells. This condition is exhibited in the 

 delta of the Rhone, where the Lavalduc Lake, which has been isolated 

 from the sea for centuries, has sunk to fifteen metres below its level. 

 It has a stratum of gypsum on the bottom, and above it is a thick 

 formation of mud, that has become a true marl where it has dried, at 

 the base of which, and at a level corresponding with the epoch at 

 which the water was nearly normal sea-water, marine shells are abun- 

 dant. It may occasionally happen that a marine estuary, in which a 

 deposit of gypsum has taken place, shall receive an accession of fresh 

 instead of salt water, and then we shall have deposits containing fresh- 

 water fossils above the gypsum. We can see from this how valueless, 

 as an argument against the theory that gypsums are products of the 

 evaporation of sea-water, is the assertion, so often put forward in that 

 guise, that gypsums are sometimes found covered with fresh-water 

 deposits. 



Similar phenomena and another illustration of our theory are ex- 

 hibited on a colossal scale in the Caspian Sea. On the eastern side of 

 that sea is the Gulf of Karabogaz, relatively small, but having a super- 

 ficial area of at least twenty thousand square kilometres. It contains 

 no living beings except some of the lower organisms, and its shores 

 are marked by a complete sterility. Its only communication with the 

 Caspian Sea is by a shallow channel which allows water to flow over 

 from the sea, but lets none back. The excessive evaporation always 

 going on in that hot and arid region causes a constant depression of 

 the level of the water in the gulf, and this induces an incessant flow 

 from the sea. In the absence of a counter-current from the Karabogaz 

 to the Caspian, all of the salt that is brought in with the inflowing water 

 remains in the Karabogaz ; the amount of salt thus regularly added to 

 the quantity already held there is not less than three hundred and fifty 

 thousand tons every twenty-four hours. It is easy to prognosticate the 

 future of this gulf. If the channel of communication is kept open, the 

 water, now nearly saturated, will continue to deposit gypsum ; but the 

 constant accession of water from the sea will prevent its reaching for 

 an extremely long time the degree of concentration that will permit 

 the deposition of salt. There will in this case be produced in the 

 Karabogaz a colossal deposit of gypsum, to which no parallel can be 

 found in the ancient formations. If, on the other hand, the channel 

 becomes obstructed, evaporation in the Karabogaz will go on more 

 rapidly, for it receives no important affluent of fresh water. Then, 

 at the end of a time which will not be prodigious, we shall have a saline 

 deposit identical with that of Stassf urt, having large masses of gyp- 

 sum at the bottom, and deliquescent salts with boracic acid at the top. 

 The latter ending is more likely to be realized ; for the level of the 

 Caspian Sea itself is falling under the excess of evaporation over the 

 supply of water brought by the rivers into it, and will at no very dis- 

 vol. xxi. 53 



