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396 DYNAMICAL GEOLOGY.  ____[Boox I 
doing, when they had sunk below the level of their outlet, began to 
grow increasingly saline. The decrease of the water and the increase 
of salinity were in direct relation to each other, until the present 
degree of concentration has been reached, as shown in the table 
(p. 398). The Great Salt Lake, at present having an extreme depth of 
less than 50 feet, is still subject to oscillations of level. When 
surveyed by the Stansbury expedition in 1849, its level was eleven 
feet lower than in 1877, when the Survey of the 40th Parallel 











































































































































































































Fic. 134.—TERRACES OF GREAT SALT LAKE, ON THE FLANKS OF THE 
Wausatco Mountains. 

examined the ground. From 1866, however, aslow subsidence of the 
lake has been in progress, consequent upon a diminution of the 
rainfall. Large tracts of flat land formerly under water are being 
laid bare. As the water recedes from them and they are exposed to 
the remarkably dry atmosphere of these regions, they soon become 
crusted with a white saliferous and alkaline deposition, which likewise 
permeates the dried mud underneath. So strongly saline are the 
waters of the lake, and so rapid the evaporation, as I found on trial, 
that one floats in spite of himself, and the under surfaces of the 
wooden steps leading into the water at the bathing-places are hung 
with short stalactites of salt from the evaporation of the drip of the 
emergent bathers.’ 
(b) Salt lakes of oceanic origin are comparatively few 
in number. In their case portions of the sea have been isolated by 
movements of the earth’s crust, and these detached areas, exposed to 
evaporation, which is only partially compensated by inflowing rivers, 
have shrunk in level, and at the same time have sometimes grown 
much salter than the parent ocean, The Caspian Sea, 180,000 square 
miles in extent, and with a maximum depth of from 2000 to 3000 feet, 
is a magnificent example. The shells living in its waters are chiefly 
the same as those of the Black Sea. Banks of them may be traced 
1 Much information regarding the Great Basin and its lakes is to be found in vol. iii, 
of Wheeler’s Survey, and in vols. i. and iy. of the Survey of the 40th Parallel. 
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