ON THE GEOLOGICAL AGENCY OF THE WINDS. 187 
the ocean was the amount by which the precipitation used to ex- 
ceed the evaporation over the whole extent of country drained 
through this now dry bed of a river. The winds have had some- 
thing to do with this ; they are the agents which used to bring 
more moisture from the sea to this water-shed than they took 
away ; and they are the agents which now carry off from that 
valley more moisture than is brought to it, and which, there- 
fore, are making a salt-bed of places that used to be covered by 
water. In like manner, there is evidence that the great Amer- 
ican lakes formerly had a drainage with the Gulf of Mexico. 
Steamers have been actually known, in former years, and in times 
of freshets, to pass from the Mississippi River over into the lakes. 
At low water, the bed of a dry river can be traced between them. 
Now the Salt Lake of Utah is to the southward and westward of 
our northern lake basin ; that is the quarter 214) whence the 
rain winds have been supposed to come. May not the same cause 
which lessened the precipitation or increased the evaporation in 
the Salt Lake water-shed, have done the same for the water-shed 
of the great American system of lakes ? 
If the mountains to the west — the Sierra Nevada, for instance — 
stand higher now than they formerly did, and if the winds which 
fed the Salt Lake valley with precipitation had, as (§ 212) I sup- 
pose they have, to pass the summits of the mountains, it is easy to 
perceive why the winds should not convey as much vapor across 
them now as they did when the summit of the range was lower 
and not so cool. 
383. The Andes, in the trade-wind region of South America, 
stand up so high, that the wind, in order to cross them, has to part 
with all its moisture 133), and consequently there is, on the 
west side, a rainless region. Now suppose a range of such mount- 
ains as these to be elevated across the track of the winds which 
supply the lake country with rains ; it is easy to perceive how the 
whole country watered by the vapor which such winds bring, 
would be converted into a rainless region. 
I have used these hypothetical cases to illustrate a position 
which any philosopher, who considers the geological agency of 
the winds, may with propriety consult, when he is told of an in- 
land basin the water-level of which, it is evident, was once higher 
than it now is ; and that position is that, though the evidences of 
