176 DISCUSSION OF THE DESICCATION QUESTION. 



extended over 127,798 acres (somewhat less than one four-hundredth part 

 of the whole area of that Territory), says : " All observers agree that the 

 climate is improving under the increasing breadth of vegetation which this 



system of cultivation has created The industrious Mormons have a 



right to expect that, as the breadth of cultivation extends, ,the rains will 

 increase in the same ratio ; that the air will become more humid as trees are 

 planted, and that a self-sustaining amount of rain-fall may in time be ob- 

 tained." It is not denied that Great Siilt Lake began to rise about the 

 year 1866, and continued to do so for several years after that time. This 

 confirms the thoroughly well authorized deductions drawn fiom a variety 

 of facts observed all through the Great Basin, namely, that the desiccation of 

 the region has not been absolutely uniform in character; but that, on the 

 other hand, it has proceeded with more or less gentle oscillations, the result 

 of which, on the whole, has been, that the lake now stands several hundred 

 feet lower than it has done since there has been any orographic change in 

 the region.* We shall have abundant occasion, farther on, to point out facts 

 indicating, in the most unmistakable manner, that the forces regulating 

 evaporation on the earth are so delicately balanced that fluctuations of these, 

 too small to be registered with our ordinary instruments, produce results 

 which are decidedly well-marked in their effect on climate. But these fluctu- 

 ations, such as tlio.se of the Great Basin Lakes within the past few years, 

 do not interfere with the general result, which slowly but surely maintains 

 itself in spite of them. 



The reason why Salt Lake has, on the whole, greatly diminished in area 

 within the recent geological period is, that evaporation more than counter- 

 balances the precipitation. This rain-fall in the valley of Salt Lake itself is 

 large, as compared with that of places in the adjacent region,! owing, no 

 doubt, in part to the existence in the immediate vicinity of so large a body 

 of water, covering, as it does, an area of about 2,400 square miles. The cul- 

 tivation and partial irrigation of less than 200 square miles of surface could 

 not, under the most favorable h3'pothesi.s, add materially to the effect pro- 

 duced by an unbroken body of water twelve times as large immediately 

 adjacent. 



The water used for irrigation in Salt Lake Valley comes from the summits 



* See ante, p. 103. 



t The rain-fall at Great Salt Lake station, as given by tlie Smithsonian observer, is about four times that at 

 Fort Bridger, about seventy-five miles distant in an easterly direction. 



