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 w^hich used to bring 

 more moisture from the sea to this water-shed than they took 

 away ; and they are the agents w^hich 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 w^ater, 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 w^ind, 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 w^atered 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 m- 

 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 



