
“Parr Il. Sxor. ii §4.] SALINE LAKES. 395 
- II, Saline Lakes, considered chemically, may be grouped as 
salt lakes, where the chief constituents are sodium and magnesium 
chlorides with magnesium and calcium sulphates; and bitter lakes, 
which usually are distinguished by their large percentage of sodium 
carbonate as well as chloride and sulphate (natron-lakes), sometimes 
_ by their proportion of borax (borax lakes). From a geological 
point of view they may be divided into two classes—(1) those 
which owe their saltness to the evaporation and concentration of 
the fresh water poured into them by their feeders; and (2) those 
which were originally parts of the ocean. 
(a) Salt and bitter lakes of terrestrial origin are 
abundantly scattered over inland areas of drainage in the heart of 
continents, as in Utah and adjacent Territories of North America, 
and in the great plateau of Central Asia. These sheets of water were 
doubtless fresh at first, but they have progressively increased in 
salinity, because, though the water is evaporated, there is no escape 
for its dissolved salts, which consequently remain in the increasingly 
concentrated liquid. 
The Great Salt Lake of Utah, which has now been so carefully 
studied by Gilbert and other geologists, may be taken as a typical 
example of an inland basin, formed by unequal subterranean move- 
ment that has intercepted the drainage of a large area, wherein 
rainfall and evaporation on the whole balance each other, and where ~ 
the water becomes increasingly salt from evaporation, but is liable 
to fluctuations in level, according to oscillations of meteorological 
conditions. The present lake occupies an area of rather more 
than 2000 square miles, its surface being at a height of 4250 feet 
above the sea. It is, however, merely the shrunk remnant of 
a once far more extensive sheet of water to which the name of 
Lake Bonneville has been given by Gilbert. It is partly surrounded 
with mountains, along the sides of which well-defined lines of 
terrace mark former levels of the water. The highest of these 
terraces lies about 940 feet above the present surface of the lake, so 
that when at its greatest dimensions, this vast sheet of water must 
have stood at a level of about 5200 feet above the sea, and covered 
an area of 300 miles from north to south, and 180 miles in extreme 
width from east to west. It was then certainly fresh, for, having an 
outlet to the north, it drained into the Pacific Ocean, and in its 
stratified deposits an abundant lacustrine molluscan fauna has been 
found. According to Gilbert there are proofs that previous to the 
great extension of Lake Bonneville, there was a dry period, during 
which considerable accumulations of subaerial detritus were formed 
along the slopes of the mountains. A great meteorological change 
then took place, and the whole vast basin, not only that termed Lake 
Bonneville, but a second large basin, Lake Lahontan of King, lying to 
the west and hardly inferior in area, was gradually filled with fresh 
water. Again another meteorological revolution supervened and the 
climate once more became dry. ‘The waters shrank back, and in so 
