176 WATER AND FOREST. 



depth precludes it being due to currents, and from the circumstance 

 of the depression occupying, as it were, the focus of the concave chalk 

 formation of eastern England, it is believed to be the point at which 

 the inland ground-waters are discharged through the chalk. Right 

 at home we have a submarine valley of great depth heading near R©- 

 dondo, with an oil well discharging, about two miles from the shore. 

 The direction In which the ground-water flows is sometimes very difH- 

 cult to trace. It does not always follow the trend of the surface con- 

 figuration. Latham, the noted sanitary engineer, in some of his 

 Investigations, found the ground-water of a valley passing partly 

 straight down the valley and part turning, going under the hills and 

 coming out on the further slope. 



The capacity of the earth to receive and convey water is all-im- 

 portant to us. The large sums that have been expended In damming 

 valleys and impounding water, the legislature that has been invoked 

 regarding reservoir sites, and the extent of agricultural interests de- 

 pendent on reservoirs, all give evidence of the appreciation of a store 

 of water. 



The pervious rocks, gravels and soils of the earth afford a time- 

 tried storage, beside which the largest surface reservoirs are small 

 affairs. The rain is the source and the earth the grand storehouse of 

 our water supplies. Whatever agencies give the rain freer access to 

 the earth should be well studied. As previously stated, the condition 

 of the ground surface is of primary importance. All soils are dependent 

 upon their top surface as to whether they will get any water to absorb 

 or not. Take an extreme case: Sand covered by an asphalt pavement; 

 a great capacity for water, but no mouth to take it in. Take an or- 

 dinary case, as exemplified by tests made at Colby, Kansas, by the 

 United States Department of Agriculture. The moisture in the soil 

 was measured at a depth of twelve inches below the surface. Meas- 

 urements were made under three separate conditions: First, a covering 

 of natural prairie sod; secondly, bare soil, cultivated; thirdly, bare 

 ground sub-soiled. The tests were continued daily throughout the 

 months of June, July, August and September. The cultivated soils 

 showed throughout the tests over twice the moisture of the soil under 

 the natural prairie top. It has been suggested that the chief cause of 

 the difference was the water taken up and evaporated by the grasses. 

 This is not supported by the records. It is obvious that there would 

 be little moisture drawn from the ground and evaporated during rains. 

 The increase of soil moisture at such times must represent the evapo- 



