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sho 
1876.] The Great Salt Lake in Former Times. 677 
before burying the mountain ridges, have filled the intermediate 
valleys, may have a maximum thickness of five thousand or six 
thousand feet. Their upper surface, water-laid and smooth, is 
the broad floor of the desert, from which arms stretch north and 
south between the fringing mountains. In longitude the plain 
measures a little over a hundred miles, and in latitude a little 
Its general level is about 4200 feet above the ocean, and 
Great Salt Lake probably occupies its greatest depression, 
though lying close to its eastern border. Its surface material is 
a fine adhesive, absolutely sterile clay, charged with chloride of 
sodium and other soluble salts, the deposit from the last expan- 
sion of the waters of the lake, an expansion so recent that the 
beach-lines formed at its culmination and during its slow subsi- 
dence are perfectly preserved on the shores of the desert. 
“ The eccentric position of the lake is evidence of the novelty 
of the present relation of altitudes of different portions of the 
plain, which is far from an equilibrium. Nearly the whole pres- 
ent increment to the desert floor comes from beyond the Wah- 
satch Mountains, and is deposited in the deltas of the Jordan, 
Weber, and Bear rivers, on the eastern margin of the lake. 
Since the lake has no outlet, but parts with its surplus by evap- 
oration, its area rather than its level tends to constancy ; and, as 
the eastern shore increases, the water will rise, pari passu, and 
encroach on the western. The continuation of this process, if 
there is no counter influence, such as a secular depression of the 
lake basin, will push the water, in a few thousand years, to the 
Western side of the desert.” ; 
aving considered the lake as it is at present, let us look at its 
Past history as elucidated by Mr. Gilbert. He considers, from a 
study of the sediments and ancient beaches, that the Great Salt 
Lake formerly included the valleys now occupied by Sevier and 
Utah lakes, and be calls.the hypothetical ancient body of water 
Lake Bonneville. “ The most conspicuous traces of Lake Bonne- 
ville are its shore-lines. At their greatest expanse the waters rose 
nearly one thousand feet above the present level of Great Salt 
“ake, and at this and numerous other stages marked their lin- 
& rings by elaborate beaches and terraces. These are very con- 
Spicuously displayed on the slopes of the Wahsatch range near 
yed on the slop 
t Salt Lake, and on the rocky islands of the lake, and have 
Attracted the attention of every observant traveler from the 
time of the explorations of Frémont and Beckwith. All the 
varied products of wave-work, as we know them on modern 
res, are represented and beautifully preserved.” 
