DRAINAGE BY BORING. 439 
of disposing of superfluous surface-water, which, however, 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 dis- 
charge, 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 Réné, in the first half of the fifteenth century, when sub- 
soil drainage was scarcely known, 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 
Rock 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. 
* Physikalische Geographie, p. 288. This method is now frequently em- 
ployed in France. Details as to the processes will be found in MaNnGon, 
Pratique du Drainage, pp. 78 et seqgg. Draining by driving down. stakes, 
mentioned in a note in the chapter on the Woods, ante, isa process of the 
same nature. 
In the United States, large tracts of marshy ground, and even shallow lakes 
of considerable extent, have been sufficiently drained not only for pasturage 
but for cultivation, without resort to any special measures for effecting that 
end. The ordinary processes of rural improvement in the vicinity, such as 
felling woods upon and around such grounds, and the construction of roads, 
the side ditches of which act as drains, over or near them, aided now and then 
by the removal of a fallen tree or other accidental obstruction in the beds of 
small streams which flow from them, often suffice to reclaim miles square of 
unproductive swamp and water. See notes on p. 20, and on cedar swamps, 
p. 208, ante. 
