December 15, 1911] 



SCIENCE 



815 



and the measure of productivity and 

 habitability. 



9. Under extensive clearing and culti- 

 vation, the store of ground water has been 

 materially depleted. Recent determina- 

 tions based on records (covering a mean 

 period of about 22 years) of 9,507 wells in 

 the nine states of Illinois, Indiana, Iowa, 

 Kentucky, Michigan, Minnesota, Ohio, 

 Tennessee and Wisconsin reveal lowering 

 of the water-table at a minimum mean rate 

 of 1.315 feet,* or with moderate allowance 

 for new wells 1.73 feet, per decade, corre- 

 sponding to an aggregate of 13.8 feet for 

 the 80 years since settlement began. This 

 lowering of the level of saturation corre- 

 sponds with an actual loss of water aver- 

 aging 5.2 inches per decade, or nearly 

 150,000,000 acre-feet annually within the 

 nine states. The loss is due largely to in- 

 creased run-off in freshets and floods, 

 which are in increasing degree wreaking 

 destruction of property and loss of life; 

 while innumerable springs and smaller 

 source streams have disappeared, and the 

 regimen of nearly all streams has been im- 

 paired. 



10. The rate of subsidence of the water- 



table varies from state to state; in those 

 enumerated it declines from 2.464 feet per 

 decade in Minnesota to 0.8 foot in Ohio, 

 while in Missouri it is but 0.43 foot. When 

 the variable rates are coordinated with the 

 geographic relations of the several states, 

 it becomes clear that the ground-water 

 reservoir of the entire interior is continu- 

 ous, that Missouri is supplied in part by 

 underflow from the Plains and Rocky- 

 Mountains, that the level in Ohio is kept 

 up in part by seepage from Lake Erie 

 (explaining that discrepancy between in- 

 flow and discharge from the lake which 

 has led to excessive estimates of evapora- 

 tion), and that Minnesota has merely lost 

 proportionately with the absence of ex- 

 ternal sources of supply — in short that 

 throughout this area of 532,402 square 

 miles (and presumably elsewhere in the 

 humid country) the reserve store of ground 

 water is not only continuous and fairly 

 conformable to the land surface but moves 

 slowly down-slope in directions generally 

 corresponding with those of the surface 

 streams. 



11. The recent researches demonstrate 

 that the surface streams of the humid coun- 



*The records are summarized in tlie table following ; the detail figures appear in the Yearbook of the 

 Department of Agriculture for 1911 under the title " Subsoil Water of Central United States.'' 



