The Paris Sewage Irrigation at Gennevilliers. 123 
. irger quantity of nitrogen and combustible organic matter is 
lound in the sewage at that spot than at Clichy. 
The sewage-water issuing at the latter outlet and at St. Denis 
respectively contain per ton : — 
CUchy. 
St. Denis. 
Grains. 
61-73 
Grains. 
2,160-55 
Combustible or volatile organic matter 
10,185-45 
21,296-85 
21,605-50 
29,939-05 
31,852-68 
53,396-45 
W hen the whole irrigation system is complete, and all the 
sewage from the three outlets is made to flow into one single 
channel, which will convey it in a flood over the proposed area, 
of suflBcient extent to absorb one hundred million tons of 
sewage per annum, the average sewage will thus convey to the 
land no less than 200 grains of fertilising matter per gallon. 
As I have already stated, no better soil could have been 
selected to test the efficiencv of the agricultural system, with the 
view of getting rid of the sewage nuisance, than the plain of 
Gennevilliers. Its immediate vicinity to the outlets, which 
saved the necessitv of constructing: anv srreat lensrth of cbstlv 
mains : its low level, which allowed the distribution of the 
sewage by gravitation, once it was raised up to the level of the 
river embankment ; the great depth of its gravelly subsoil, 
through which the water easily percolates to the water-bearing 
stratum, the level of which, from its direct communication 
with the river, never rises above it, except in case of great 
floods, when the natural drainage is taxed bevond its power of 
discharge : — all these advantages and favourable circumstances, 
could not fail to help the experiment to a highly successful 
issue. As might have been expected, the water, after perco- 
lating through the gravelly soil, was found at its effluence into 
the river in as great a state of purity as could be desired. The 
soil acts as a natural filter of great power, through which the 
water becomes easily aerated and oxygenised. 
To those favourable elements must be added the utterly barren 
nature of the tract of waste land comprising the plain of Gen- 
nevilliers, to which, however, its proximitv to the capital would 
give a very high value, if it could onlv be made productive. 
This transformation, sewage alone could accomplish ; and market- 
gardeners, nurserymen, and agriculturists, were not slow in 
accepting the proffered boon. 
L nfortunately the available area is by no means adequate to 
