DE RAXCE : UXDERGROUND WATER-SUPPLY AXD RIVER FLOODS. 203 
down the water which would have swamped the surface into the 
limestone beneath, along which it travels, until the limestone is 
intersected by a valley, and the water tumbles over the limestone and 
shale beneath and forms a ready-made river. 
Wells or shafts have been sunk in a few instances in England, but 
more numerously on the Continent, for the purpose of acting 
as artificial swallow-holes, such shafts are known as dumb-wells," 
and can often be found to effectually drain a small property, at a 
fraction of the expense that would have been necessary to obtain an 
efficient discharge at a distant point. If ever they should be carried 
out on a large scale, they will materially reduce floods, and increase 
the dry-weather flow of streams. 
The iMillstone Grit series consists of an alternation of water 
holding, and water supporting material, allowing a very small pro- 
portion of the rainfall to be wasted, most of the percolation being 
returned as springs into the same river basin, and the shale forming 
an impermeable base for reserviors, it has given a valuable supply of 
water to all the great gravitation waterworks of the Xorthern Counties. 
The shale causes the rainfall, which would otherwise have escaped 
in bursting floods, to maintain the dry weather flow of the streams, 
the size of the reservoirs is not excessive, owing to their being 
steadily replenished by springs. In nearly all the waterworks in 
these districts provision has been made for the wants of the mill- 
owners, formerly supplied by these streams, by the construction of 
enormous "compensation reservoirs," delivering, in the case of 
of Manchester, fifteen million gallons a day. Mill-owners have been 
enormously benefited in having a regular daily supply sent down to 
them, instead of having to depend upon the capricious volume for- 
merly coming to them, influenced by climatic variations of draught 
and flood. In many cases, the provisions and engagements, entered 
into by Corporations with the mill-owners, appear to be too onerous, 
and were a "Conservancy Board " to be constructed, Parliamentary 
relief should be given from the penalty clauses for not being able to 
supply during years of exceptional draught, when it was the opinion 
of the Conservancy Board that the Corporation had done all that 
was reasonable to expect, and Corporations no longer compelled, after 
