Davis. 
824 
[January 18 , 
been given ; 1 it occupied tbe eastern depression of the Great 
Basin, and was over two hundred miles long, north and south, 
and one hundred broad ; in depth it was probably over twelve 
hundred feet. Its shore contoured irregularly around the moun- 
tain boundaries, and from its surface rose islands to a height of 
several thousand feet. A similar lake, named Lahontan , 2 existed 
at the same time in the western depression, with an outlet prob- 
ably southward into the Colorado. 
The drying up of these lakes, a process of many thousands of 
years, is now much nearer its final stage than its beginning. Great 
Salt Lake is the only considerable remnant of Bonneville, of 
whose volume it is now less than a hundredth part, being in 
depth only fifty feet. Lahontan, whose surface was greatly 
broken by the western Basin Ranges, is reduced to several inde- 
pendent salt lakes, Carson, Humboldt, Walker’s, Winnemucca and 
Pyramid, besides some shallow “ sinks ” that contain water during 
only part of the year. 
Bonneville and Lahontan were the last of a series of great 
lakes that have been enclosed by the ranges of our Cordilleras since 
the beginning of Tertiary times . 3 They successively lasted long 
enough to receive great quantities of sediment from the surround- 
ing mountains, and some of these deposits are now famous for the 
fossils they have preserved. Their disappearance was brought 
about by their filling up, by a tilting of their basins, by the 
growth of new mountain boundaries, or by the wearing down of 
their outlets ; and possibly early periods of dessication had a share 
in producing these changes. Great Salt Lake is more distinctly 
than any other the direct descendant of its greater freshwater 
ancestor, and the well marked terraces at its former levels, the 
extreme flatness of its shores and the indecision of its boundary, 
the exceedingly small depth ratio and the high degree of salinity, 
all combine to make it a perfect example of its species. 
The other Great Basins of -the present time may be rapidly. 
1 Gilbert, U. S. Geog. Surveys W. of 100th Meridian, in, 88. King, U. S. Geol. 
Expl. 40th. Parallel, I, 490, 525. 
2 King, i, 504. 
3 King, i, 445. 
