38 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
reason to doubt that the water artificially let into the Marl- 
%J 
stone would be equally pure, and there are several decided 
advantages in collecting and storing the water in underground 
reservoirs rather than in open ones, which must be more or 
less evident to everyone. 
Flood water and river water in the early stages of a flood 
are more impure than at other times, owing to the washing 
of lands on or in which impurities have been accumulating, 
and the displacement of water from springs or subsoils where 
it has been stagnating, though in the later stages of a flood 
river water appears to be more than usually pure.* Notwith¬ 
standing this, I think I may claim that the water to he utilised 
by this scheme would not , in the first instance, be more impure than 
some which is now used for the supply of towns , after artificial 
filtration, whilst the arrangements for purification are much 
more perfect than any adopted by these towns ; let me call 
attention to them. 
There are special arrangements for filtering the water before it 
reaches the well. The flood water can only enter the dumb- 
well after passing over soil covered with vegetation, then 
through soil or sand and drain pipes, or, if it comes from the 
river, through a considerable amount of sand or gravel, and 
by either of these processes it would be completely clarified. 
The water which is now obtained from the river gravel 
is perfectly clear and bright, and contains, as a rule, 
nothing actually injurious, though the quantity of nitrates 
present would be, in this case, interpreted as a proof of 
previous contamination. This speaks well for the bed, though 
not for the water now contained in it, but with a larger and 
more rapid circulation of water this suspicious character 
would diminish, and the total solids become less. 
The water would be well filtered in the wells themselves by a 
quantity of sand and gravel at least five or six times as great 
as that considered sufficient for the filtration of Thames water 
by the London Water Companies. 
The water would be again filtered in the Marl stone itself, a 
filtration of a most perfect kind, and probably quite sufficient 
without any artificial aid. I have no hesitation in saying 
that there is no artificially collected water in this country so 
well filtered as this would be before reaching the pumping 
station. 
* For particulars on this and other points connected with rivers, 
see “ River Water,” by C. Meymott Tidy, M.B., M.A., M.S. Journal 
of Chemical Society, May, 1880. 
