. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 151 soil of the surrounding highei' ground. This is because the water level being higher, tends to lift by hydrostatic pressure, some water up into the soil of the lower fields, that is to say, the lower fields are supplied from below with water which falls upon the higher ground. - — :^J^^iV"'*^;':i^f'^| ±': ir. 'V_V:'<^-^/t^^:JX''-^:x^^^. 'm^^^^^A Fig. 2. Stowiug the geologic structure favorable to natural subirrigation. Not all low lands adjacent to high areas are equally sub- ject to the n
. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 151 soil of the surrounding highei' ground. This is because the water level being higher, tends to lift by hydrostatic pressure, some water up into the soil of the lower fields, that is to say, the lower fields are supplied from below with water which falls upon the higher ground. - — :^J^^iV"'*^;':i^f'^| ±': ir. 'V_V:'<^-^/t^^:JX''-^:x^^^. 'm^^^^^A Fig. 2. Stowiug the geologic structure favorable to natural subirrigation. Not all low lands adjacent to high areas are equally sub- ject to the natural subirrigation referred to, for differences in the structure of the soil necessarily modify the move- ment of the rain which has entered the ground. The structure best suited to the storing of water in the high lands and the giving of it out gradually to the adjacent lower areas is represented in Fig. 2 where the surface of the lower areas is covered to a depth of three to four feet with clay soil and subsoil; on the highland this mantle passes, by degrees, through a porous, sandy and gravelly clay into a sand and gravel or pure sand of considerable depth into which the water percolates rapidly, and out of which it flows laterally with comparative ease toward and below the adjacent lower areas. This type of geological structure is very common in many parts of Wisconsin and other sections of the United States which are heavily mantled with the deposits of the glacial epoch. The ter- minal morains of this and other states are water reservoirs of great extent and capacity into which the rains sink at once and are there stored under conditions of the least possible loss by surface evaporation, to be given out grad- ually in restricted but innumerable areas. Heavy rains, which in other sections are lost to agriculture in destruc- tive floods, are here safely and economically stored and it is these very many naturally subirrigated tracts to which. Please note that these imag
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