1903 



FORESTRY AND IRRIGATION 



per cent. The most productive water- 

 bearing rocks, however, are found to be 

 the porous sandstones, and in some cases 

 limestones, whose inner texture has been 

 chemically dissolved. 



The popular idea of underground 

 waters is derived from the rivers of 

 copious discharge found in the Mam- 

 moth and other caves ; but this idea is 

 erroneous, as such streams, though of 

 great local importance, are compara- 

 tively rare. The great mass of ground 

 water slowly percolates through sand 

 and gravel deposits, sandstone, and 

 other porous material under a wide 

 extent of territory. Though its motion 

 carries it but a fraction of a mile in a 

 year, this ground water is so widespread 

 and often so accessible as to be of the 

 greatest economic importance. 



The knowledge of the underflow that 

 exists beneath the gravel of all river 

 valleys has been taken advantage of in 

 arid sections of the West, where the 

 running dry of streams deprives irriga- 

 tors of their water supply. By exca- 

 vating to bed rock in river gravels and 

 building an impervious barrier across 

 the channel, these underground waters 

 are saved in sufficient quantities to be 

 of great value to the farmer. A nota- 

 ble subsurface dam of this kind has 

 been constructed on the Pacoima Creek, 

 California, to furnish \vater for irriga- 

 tion and domestic use. 



Deep zones of flow are a most impor- 

 tant feature of the movements of under- 

 ground waters, and open up an interest- 

 ing field for investigation. The won- 

 derful artesian basin of North Dakota 

 and South Dakota, which has proved 

 such an important factor in the economic 

 development of these states, forms one 

 of the illustrations used by Professor 



Schlichter in the explanation of deep- 

 seated underflows. 



A cross-section of this part of the 

 country clearly shows the interesting 

 fact that the water which comes to the 

 surface in the gushing wells of the 

 Dakotas travels underground all the 

 way from the Black Hills and Rocky 

 Mountain slopes, in the water-bearing 

 strata kno\vn as the Dakota sandstone. 

 Another illustration of extensive basins 

 due to deep underground flows is found 

 in Wisconsin, where an extensive area 

 of water-bearing rocks, nearly 1,000 

 feet thick, conducts w r ater of singular 

 purity under large areas of the state. 



It must be borne in mind that there 

 is a limit to the amount of water which 

 can be drawn from an artesian basin, 

 and that there is no such thing as an 

 inexhaustible underground supply. The 

 gradual failure of the wells which sup- 

 ply the city of Denver clearly illustrates 

 this fact. So great a demand was made 

 upon this basin between the years 1884 

 and 1890 that it has been estimated 

 that, if all the wells were now T plugged, 

 the water-bearing strata of the basin 

 would require forty years to recover 

 the saturated conditions which existed 

 w 7 hen the first well was sunk. 



The stud} 7 of underground water in 

 its relation to the effective water supply 

 of the country is one of the most im- 

 portant departments of the work of the 

 United States Geological Survey. It 

 is carried on in the arid regions, where 

 w^ater for irrigation is of the greatest 

 value ; in the middle w r est, where graz- 

 ing and successful farming largely de- 

 pend on it, and in the east, where an 

 unpolluted supply for domestic and 

 municipal use is yearly becoming a more 

 serious problem. 



RECENT PUBLICATIONS 



The Forests of Upper India and Their Inhabitants. 

 By THOMAS W. WEBBER, late Forest Sur- 

 veyor for the Northwest Provinces and 

 Deputy Conservator of Forests in the Cen- 

 tral Provinces and Gorakhpur. Published 

 by Edwin Arnold, London, and Longmans, 

 Green and Co., New York. 

 The book is an account of the author's life in 



the hills of India, and relates to a period of 

 years shortly after the great mutiny in 1857. 

 It describes briefly the forests of the Northwest 

 and Central Provinces, but is confined mostly 

 to a description of the people and animals 

 which inhabit these regions. It is remarked 

 in the preface that in those days the knowl- 

 edge of forestry, from a French or German 



