. The soil, its nature, relations, and fundamental principles of management . arrows, the lowerportion of the field is subject to sub-irrigation, the waterunder the higher ground tending, through its greaterhydrostatic pressure, to move toward and up into thesoil of the lower field. Sub-irrigated lands of this character occur in manyplaces and under conditions where the geological struc-ture is much as represented in Fig. 42. In these cases Sub-Irrigate J Lands. 26a the surrounding high lands are more or less open intexture, so that the rains percolate into them readily,but drain away slowly,
. The soil, its nature, relations, and fundamental principles of management . arrows, the lowerportion of the field is subject to sub-irrigation, the waterunder the higher ground tending, through its greaterhydrostatic pressure, to move toward and up into thesoil of the lower field. Sub-irrigated lands of this character occur in manyplaces and under conditions where the geological struc-ture is much as represented in Fig. 42. In these cases Sub-Irrigate J Lands. 26a the surrounding high lands are more or less open intexture, so that the rains percolate into them readily,but drain away slowly, making the adjacent flat landsmore or less springy or marshy, and only fit for tillageafter they have been underdrained. Such lands, however,once they are underdrained, become very valuable on ac-jount of their abundant water supply. Nor is this type ofland at all uncommon in the northern part of the UnitedStates. Indeed, the glacial hills referred to in an earlierchapter are impounding reservoirs of great extent andcapacity, into which the rains sink immediately, and are. Fig. 41.— Showing the rate of change in the level of the ground waterafter a rainfall of .87 inches. there stored, under conditions of least possible loss byevaporation, to be given out gradually in restricted butinnumerable areas. Heavy rains which in countries ofdifferent structure are lost to agriculture in disastrousfloods are here safely and economically stored; and it isto this stored water escaping slowly again from theground, more than to direct rainfall and flat topography,that we owe the existence of our innumerable smalllakes, and the many areas of swamp and lowland pas-tures so characteristic of glaciated regions. These manynaturally sub-irrigated tracts are especially promising formarket gardening and other forms of intensive farming. 262 The Soil. There is another phase of this question to which atten-tion should be called. There are many and extendedtracts of country underlaid by artesian wat
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectsoils, bookyear1895
