
oo A 
400. DYNAMICAL GEOLOGY. [Boo IIT. 
of crystals of common salt and gypsum. Beds of similar saliferous 
and gypsiferous clays with bands of gypsum rise along the slopes — 
for some height above the present surface of the water, and mark 
the deposits left when the Dead Sea covered a larger area than it 
now does. Save occasional impressions of drifted terrestrial plants, 
these strata contain no organic remains.’ Interesting details regard- 
ing saliferous deposits of recent origin on the site of the Bitter Lakes 
were obtained during the construction of the Suez Canal. Beds of 
salt interleaved with lamine of clay and gypsum crystals were found 
to form a deposit upwards of 30 feet thick, extending along 21 miles 
in length by about 8 miles in breadth. No fewer than 42 layers of — 
salt, from 3 to 18 centimetres thick, could be counted in a depth of 
2:46 metres. A deposit of earthy gypsum and clay was ascertained to 
-have a thickness of 367 feet (112 metres), and another bed of nearly 
pure crumbling gypsum to be about 230 feet (70 metres) deep.” : 
The desiccated floors of the great saline lakes of Utah and Nevada 
have revealed some interesting facts in the history of saliferous 
deposits. ‘The ancient terraces marking former levels of these lakes 
are cemented by tufa, which appears to have been abundantly formed 
along the shores where the waters of the brooks mingled with that 
of the lake and immediately parted with their lime. Even at present 
oolitic grains of carbonate of lime are to be found in course of forma- 
tion along the margin of Great Salt Lake, though carbonate of lime 
has not been detected in the water of the lake, being at once precipi- 
tated in the saline solution. The site of the ancient salt lake which 
has been termed Lake Lahontan, displays areas several square miles 
in extent covered with deposits of calcareous tufa twenty to sixty and 
even one hundred and fifty feet thick. This tufa, however, presents a 
remarkable peculiarity. It is sometimes almost wholly composed of 
what have been determined to be calcareous pseudomorphs after 
gaylussite (a mineral composed of carbonates of calcium and sodium 
with water)—the sodium of the mineral having been replaced by 
calcium. When this tufa was originally formed, the waters of the 
vast lake must have been bitter, like those of the little soda lakes 
which now lie on its site—a dense solution {in which carbonate of 
soda predominated. On the margin of one of the present Soda 
Lakes crystals of gaylussite now form in the drier seasons of the 
year. Yet no trace of carbonate of lime has been detected in the 
water. The carbonate of lime in the crystals must be derived 
from water, which on entering the saline lakes is at once deprived 
of its lime.® 
§ 5. Terrestrial Ice. 
Fresh water, under ordinary circumstances, when it reaches a 
temperature of 32° Fahr. passes into the solid state by crystallizing 
' Lartet, Bull. Soc. Géol. (2nd sér.), xxii. p. 450, et seq. 
? Lesseps, Ann. Chim, et Phys. (5), iii. p. 139. Bader, Verhandl. K. K. Reichsanst. 
1869, p. 288. 
® King, Hxploration of the 40th Parallel, i. p. 510. 
