UNDER-DRAINING. 
361 
is never so regularly inclined as to permit water to flow freely 
over it. There are, even on the hillsides, many small ridges 
and depressions, partly belonging to the original distribution 
of the soil, and partly occasioned by irregularities in the 
growth and deposit of vegetable matter. These, in the hus¬ 
bandry of nature, serve as dams and reservoirs to collect a 
larger supply of moisture than the spongy earth can at once 
imbibe. Besides this, the vegetable mould is, even under the 
most favorable circumstances, slow in parting with the hu- 
midity it has accumulated under the protection of the woods, 
and the. infiltration from neighboring forests contributes to 
keep the soil of small clearings too wet for the advantageous 
cultivation of artificial crops. For these reasons, surface drain¬ 
ing must have commenced with agriculture itself, and there is 
probablv no cultivated district, one may almost say no single 
field, which is not provided with artificial arrangements for 
facilitating the escape of superficial water, and thus carrying off 
moisture which, in the natural condition of the earth, would 
have been imbibed by the soil. 
The beneficial effects of surface drainage, the necessity of 
extending the fields as population increased, and the incon¬ 
veniences resulting from the presence of marshes in otherwise 
improved regions, must have suggested at a very early period 
of human industry the expediency of converting bogs and 
swamps into dry land by drawing off their waters; and it 
would not be long after the introduction of this practice before 
further acquisition of agricultural territory would be made by 
lowering the outlet of small ponds and lakes, and adding the 
ground they covered to the domain of the husbandman. 
All these processes belong to the incipient civilization of 
the ante-historical periods, but the construction of subterranean 
channels for the removal of infiltrated water marks ages and 
countries distinguished by a great advance in agricultural 
theory and practice, a great accumulation of pecuniary capital, 
and a density of population which creates a ready demand and 
a high price for all products of rural industry. Under-drain¬ 
ing, too, would be most advantageous in damp and cool cli- 
