110 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
These dumb wells would all be situated in the valleys, 
and would generally require to be cut through a little allu¬ 
vium and river gravel, and through the Upper and Middle 
Lias. The wells might be lined with brick, and then filled 
up with coarse gravel, broken brick, or any good porous 
material to within 85ft. or 40ft. of the top, the material to 
get finer towards the top, in imitation of the filter beds of 
the London Water Companies. The depth of 85ft. to 40ft. 
not filled in with gravel is given to enable the water running 
in from the river gravel, as well as that from the surface, 
where such water is desirable, to have a good fall, whereby 
it may be effectually aerated before entering the chief filter 
bed. Some large stones might be placed at the top of the 
sand to prevent the latter from being much disturbed by the 
falling water. The river gravel is so commonly met with 
along the Nen Valley that very great use might be made of 
it in such a scheme as is here being described. Sometimes 
this gravel is capped by 12ft. to 14ft. of alluvium, an earthy 
kind of clay containing much organic matter, and very 
impervious to water ; at other times the gravel comes nearly 
or quite to the surface, but there is every reason for believing 
it to be a fairly continuous bed. The flat land on each side 
of the River Nen eastward of Northampton gives almost the 
exact limits of the alluvium, or river gravel, or both—that 
is, the part which is so liable to floods has below it a porous bed 
which may be utilised for the mitigation of floods. The gravel 
frequently extends beyond and above the alluvium, and forms a 
kind of fringe to the valley, as described in a previous page. 
(See Plate II.) Since, then, we have a porous bed, several feet 
in thickness, existing very little below the ground which is 
now so commonly flooded, it would not be a difficult matter 
to make a number of artificial openings into it from the 
surface, and fill them up with gravel, so as to put the primary 
well into good Communication with the source of its supply— 
flood-water. At the present time water obtained from the 
river gravel is clear, and free from suspended impurities, and 
would still be so if this plan were adopted, so that there 
would be little or no silting up of the dumb wells. In some 
places where it might be desirable to construct a dumb well 
the river gravel would not lend itself for the purpose ; this 
would be the case in the northern branch of the Nen. The 
difficulty might be got over by making six or more radiating 
channels from the well to a slight depth, in which would be 
placed large drain pipes, these to be covered over with gravel 
and the turf replaced. The precautions here mentioned 
would secure the wells from any rapid silting up, although 
