36 Mr. Farey on Overflowing Wells and Bore-holes. 
coast, including parts of the adjoining 
counties, between Cromer. on the 
north, and Reculver (or Sandown) on 
the south, rise higher,—for the most 
part considerably higher,—than the 
surface of the London clay; that there- 
fore the water from the joints of the 
chalk, might be expected to rise and 
overflow the top of a deep well or bore- 
hole, in any part of the London clay 
district; which evidently seems to be 
the opinion of your correspondent 
Mr. S.S. and of some others who have 
written on the subject. 
But it is necessary to take into the 
account, several very deeply excavated 
valleys on the borders of the London 
clay, where the clay is reduced to a 
thin edge, in the bottoms of such val- 
leys; through which excavations the 
chalk waters, overflowing there at the 
surface, are enabled spontaneously to 
flow, on to and across the clay strata, 
in their course towards the tidal 
estuary of the Thames ; the principal 
of which excavations is that for the 
Thames itself, just below the town of 
Maidenhead; those for its southern 
tributary streams are,—for the Wey, 
about three miles below Guilford ; for 
the Mole, about two miles below Lea- 
therhead; for the Wandle, about a 
mile above Mitcham, &c. For the 
northern branches of the Thames, the 
principal excavations on the edge of 
the clay strata are only two, viz. for 
the Coln, near Uxbridge; and for the 
Lea, about a mile below Ware, 
The two last natural outlets for the 
northern chalk waters, enable a great 
part of the Hertfordshire chalk-waters 
to escape, and flow on to the London- 
clay strata, in their way to the Thames ; 
the main bodies of these waters proceed 
in their natural courses to the Thames, 
at Staines and at Blackwall: but other 
parts of each af these streams have 
been diverted by art, at no great dis- 
tances from their outlets, and are con- 
veyed towards London, from near Ux- 
bridge by the Grand-Junction and 
Regent’s Canals, and from near Ware, 
by the New River. On the south-cast 
of the town of Islington, the former of 
these artificial conduits, for the over- 
flowings of the chalk waters, has been 
lately made to pass in a tunnel, under 
the other of these conduits ; and there- 
by we are furnished, with the ready 
means of roughly comparing the height 
of the water in these two conduits, not 
only where they cross, as above-men- 
tioned, but at their sources near 
Uxbridge and near Ware. 
[ Aug. 1, 
Allowing for the rise of four locks, 
which occur in the Regent’s Canal be-; 
tween the Islington tunnel and the 
Regent’s Park, and for two other 
locks which occur on the Grand Junc- 
tion, between Bull-bridge and the 
Uxbridge outlet ; and allowing, in like 
manner, for the elevation of the New- 
River water, above the water in the. 
tunnel beneath it, and for the very 
easy rise which the surface of the New 
River (as a very slowly-running 
stream,) presents, from Islington to 
its source near Ware: it will hence 
appear, that these two principal natu-. 
ral vents for the chalk-water, on the 
north-west and north of London, are 
nearly on one level; and the course 
on the map, of these two artificial wa- 
ter-conduits, meeting at Islington, 
furnishes a visible and important line 
of demarkation across Middlesex, for 
distinguishing (with some few local 
exceptions, where these conduits are 
either embanked, or deep-cut, or tun- 
nelled,) the places, situated south- 
ward of such line, as lying below the 
chalk-water level, (as Tottenham is 
situated below the course of the New 
River,on theeastof the latter, from those 
other and higher-lying places, to the 
northward of this line of demarkation ; 
where, consequently, there can be no 
reason for expecting that a well or a 
bore-hole should overflow on the sur- 
face; and where, in point of fact, 
none do overflow, as far as I know. 
In this district of Middlesex, situated 
above the chalk-water level, there are 
numerous modern wells, of great 
depth most of them, in which the wa- 
ter has risen, and a supply of it per- 
manently stood, a great many feet 
above the places, where such waters 
were first tapped, by the augers used 
in the bottoms of such wells, by the 
well-sinkers; and perhaps, where these 
operations have been judiciously and 
well performed, the water has in ge- 
neral risen, to the level of the natural 
outlets above-mentioned. 
The heights of two others of the be-, 
fore-mentioned natural outlets of the 
chalk-waters, viz. that near Maiden- 
head, and that below Guilford, are 
probably not greatly different from the 
height of those two northern outlets 
already described; but this being a 
matter of great practical importance, 
towards demarking the entire district, 
around London, to the westward and 
southward, wherein overflowing wells 
or bore-holes might reasonably be ex- 
pected to be obtained; I beg to sug- 
gest 
