= - — r : 4 : y - -. 7 3 TSS eee 
398 ‘DYNAMICAL GEOLOGY. [Book TI. 
called the Karaboghaz, which is connected with the middle basin of 
the Caspian by a channel 150 yards wide and 5 feet deep. Through 
this narrow mouth there flows from the main sea a constant current, 
which Von Baer estimated to carry daily into the Karaboghaz 
350,000 tons of salt. An appreciable increase of the saltness of that 
gulf has been noticed: seals, which once frequented it, have forsaken 
its barren shores. Layers of salt are gathering on the mud at the 
bottom, where they have formed a salt-bed of unknown extent, and 
the sounding-line, when scarcely out of the water, is covered with 
saline crystals.? 
The following table shows the proportion of the saline materials 
in the waters of some salt lakes: 









A 4 = 
Caspian Sea. & Bop yt 
Ha Ea eal Ms 
Constituent (except - ‘3 | Great Salt Lake, | WH eis @ 
where otherwise stated).| Near mouth of 2 5 Utah. (O. D. a2", Ss 
R. Ural At Baku Bo Allen.) Sad! § 
(Gobel). (Abich). yy ae 
= a) 
Chloride of Sodium. .| 0°3673 8°5267 23°928) 11°8628 3°83 3°6372 
- Magnesium] 0°0632 0°3039 1°736 1°4908 19°75 | 15°9774 
39 Calcium .| 0°0013 (MgCO3) ee ee ey ‘ 4°7197 
» Potassium .| 0-0076 trace . 0°101 (“chierise) 0-23 | 08379 
Bromide of Magnesium | trace. 50 0°005 oo be 0°8157 
Sulphate of Calcium .j| 0°0490 1°0742 0°042} 0°0858 ee 0°0889 
‘ Potassium .| 0°0171 (CaCO3) 0°0554 (CaCO3)| -- 0°5363 an on 
Magnesium] 0°1237 3°2493 0°346) 0°9321(~NaSO,4)| 5°32 Oe 
Water . . . « .|99°3806 86°7905 73°842| 85°0060 70°87 | 73°9232 
100°0000 100°0000 
100"000) 100°000 100: 000|100°0000 

Deposits in Salt and Bitter Lakes.—The study of the pre- 
cipitations which take place on the floors of modern salt lakes is 
important in throwing light upon the history of a number of 
chemically formed rocks. The salts in these waters accumulate 
until their point of saturation is reached, or until by chemical re- 
action they are thrown down. The least soluble are naturally the 
first to appear, the water becoming progressively more and more 
saline till it reaches a condition like that of the mother liquor of 
a salt work. Gypsum begins to be thrown down from sea-water 
when 37 per cent. of water has been evaporated, but 93 per cent. of 
water must be driven off before chloride of sodium can begin to 
be deposited. Hence the concentration and evaporation of the 
water of a salt lake having a composition like that of the sea 
would give rise first to a layer or sole of gypsum followed by one 
of rock-salt. ‘This has been found to be the normal order among 
the various saliferous formations in the earth’s crust. But gypsum 
may be precipitated without rock-salt, either because the water was 
diluted before the point of saturation for rock-salt was reached, 
* Von Baer, op. cit. (1855-6). See also Carpenter, Journ. Roy. Geog. Soc. xviii. No. 4. 
For the composition of the water of salt and bitter lakes, see the analyses collected by 
Roth in his “*‘ Chemische Geologie,” i. p. 463, et seq. 

