362 
BE AIN AGE BY BOEING. 
mates, 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 neces¬ 
sary, at least apparently 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 of disposing of superfluous surface water, which, how¬ 
ever, can rarely be practised, because the necessary conditions 
for its employment are not of frequent occurrence. Whenever 
a tenacious water-holding stratum rests on a loose, gravelly 
bed, so situated as to admit of a free discharge of water from 
or through it by means of the outcropping of the bed at a lower 
level, or of deep-lying conduits leading to distant points of 
discharge, superficial waters may be carried off by opening a 
passage for them through the impervious into the permeable 
stratum. Thus, according to Bischof, as early as the time of 
King Bene, in the first half of the fifteenth century, the plain 
of Paluns, near Marseilles, was laid dry by boring, and Wittwer 
informs us that drainage is effected at Munich by conducting 
the superfluous water into large excavations, from which it 
filters through into a lower stratum of pebble and gravel lying 
a little above the level of the river Isar.* So at Washington, 
in the western part of the city, which lies high above the rivers 
Potomac and Bock Creek, many houses are provided with dry 
wells for draining their cellars and foundations. These extend 
through hard tenacious earth to the depth of thirty or forty 
feet, when they strike a stratum of gravel, through which the 
water readily passes off. 
This practice has been extensively employed at Paris, not 
merely for carrying off ordinary surface water, but for the dis- 
* Physilcalische Geographie , p. 288. Draining by driving down stakes, 
mentioned in a note in a chapter on the woods, ante, is a process of the 
same nature. 
