1882 .] 
323 
[Davis. 
usually cut off from a direct and plentiful supply of oceanic 
moisture by the mountains that enclose them, and in the present 
relation between our ocean-area and the sun’s heat, evaporation 
from the extended surface of great lakes generally equals their 
moderate rain and river supply before the maximum volume is 
attained, and no overflow is then possible. An area is taken so 
that supply and loss are equal, and as there is then no way of 
carrying off the saline matter brought in solution by the streams, 
it remains and accumulates, and the w r ater turns brackish or salt. 
The interior basins have thus lost, through the recent general 
change toward a dryer climate , 1 the great bodies of water with 
which they were largely covered during modern geological times ; 
their lakes have been reduced to small dimensions or have quite 
disappeared, leaving salt or alkaline deposits in their place. When 
near extinction, they are very shallow conqpared to their surface 
measures, their shape is irregularly oval, the shore-line is ill-defined 
and shifts with the seasons, and their salinity may be near or at 
saturation. At certain elevations above their level, are terraces 
or benches marking old shore-lines that were maintained for some 
time by a balance of supply and loss , pauses in the dwindling 
away of the lake ; the highest of these generally shows the level of 
overflow, and by following around its circuit the outlet may be 
discovered. 
Great Salt Lake is an example of the species in its ordinary, 
reduced condition. In the Great Basin of Utah and Nevada 
there are two principal areas of depression ; an eastern, bordering 
the Wahsatch Mountains, and a western, at the foot of the Sierra 
Nevada, with straggling north and south ranges between them, 
and it is only here that an approach to definite knowledge has 
been gained of the early area of lakes of this class. Near Salt Lake 
City the terraces of earlier shore-lines have long been observed, 
the highest of which stands in remarkable distinctness over nine 
hundred feet above the present lake ; and recently this has been 
traced with considerable care around the greater part of its 
course, and to the north a probable outlet into Snake Biver 
has been discovered. To the fine sheet of water, at whose margin 
this high terrace was formed, the name of Lake Bonneville has 
1 J. D. Whitney, Climatic Changes of Later Geological Times, Cambridge, 1882. 
