438 DRAINING OF SWAMPS. 
over it. There are, even on the hillsides, small ridges and de- 
pressions, 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 husbandry of 
nature, serve as dams and reservoirs to collect a larger supply 
of moisture than the spongy earth can at once imbibe. Be- 
sides this, the vegetable mould is, even under the most favor- 
able circumstances, slow in parting with the humidity it has 
accumulated under the protection of the woods, and the infil- 
tration from neighboring forests contributes to keep the soil of 
small clearings too wet for the advantageous cultivation of 
artificial crops. For these reasons, surface draining must have 
commenced with agriculture itself,and there is probably 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. 
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 climates, 
where evaporation is slow, and upon soils where the natural 
inclination of surface does not promote a very rapid flow of the 
surface-waters. All the conditions required to make this mode 
of rural improvement, if not absolutely necessary, at least 
profitable, exist in Great Britain, and it is, therefore, very 
natural that the wealthy and intelligent farmers of England 
should have carried this practice farther, and reaped a more 
abundant pecuniary return from it, than those of any other 
country. ‘ 
Besides superficial and subsoil drains, there is another method 
