68 LANDS OF THE ARID REGION OF THE UNITED STATES. 
increased size, in the face of an evaporation that yearly removes a layer 
several feet in depth. The same compensatory principle that restricts the 
“limited oscillation” would quickly restore the equilibrium between inflow 
and evaporation, in whatever manner in was disturbed. 
CLIMATIC THEORY. 
It is generally supposed that the change is a phenomenon of cli- 
mate, and this hypothesis includes harmoniously the increase of streams 
with the increase of lake surface. By some it is thought that the climate 
of the district is undergoing, or has undergone, a permanent change; and 
by others that the series of oscillations about a mean condition which char- 
acterizes every climate has in this case developed a moist phase of excep- 
tional degree and duration. The latter view was my own before I became 
aware of the features of the ancient storm line, but it now appears to me 
untenable. That a variable surface of evaporation, which had for a long 
period recognized a limit to its expansion, should not merely exceed that 
limit, but should maintain an abnormal extent for more than a decade, is in 
a high degree improbable. 
It is far more probable that one of those gradual climatic changes, of 
which geology has shown the magnitude and meteorology has illustrated 
the slowness, here finds a manifestation. ‘The observed change is apparently 
abrupt, and even saltatory ; but of this we cannot be certain, since it is 
impossible from a record of only thirty years to eliminate the limited oscil- 
lation. It is quite conceivable that were such elimination effected, the 
residual change would appear as a continuous and equable increase of the 
lake. However that may be, a certain degree of rapidity of change is 
necessarily involved, for the climatic change which is able in a decade 
to augment by a sixth part the mean area of evaporation cannot be of 
exceeding slowness. If we can ascertain how great a change would be 
demanded, it will be well to compare it with such changes as have been 
observed in other parts of the country, and see whether its magnitude is 
such as to interfere with its assumption. 
The prevailing winds of Utah are westerly, and it may be said in a 
general way that the atmosphere of the drainage basin of Great Salt Lake 
