1823.} 
ing earth; and, in short, entertain but 
faint hopes of ever seeing a large tun- 
nel executed under a wide river by 
this or any other means, if subterra- 
nean perforation is resorted to. At 
the same time, the wondertul advan- 
tages that would attend an archway ef 
this description, occasions me to regret 
that the practicable and certain me- 
thods of elfecting this object, which 
have long ago been pointed out, have 
not received attention from the public. 
One of these methods, applicable to 
situations where the site of the river 
could net be changed, on account of 
houSes on its banks, (as at Rother- 
hithe,) or en account of the height of 
those banks, consists in excluding the 
water of the river, in successive por- 
tions of its breadth, either by coffer- 
dams of tall and close piling, or else 
by an immense tub-like caison, whilst 
the river’s bed is deepened within such 
coffer-dam or caison, and a portion of 
the arch formed, and securely covered 
over, at no greater depth below the 
water than such security requires; by 
which means much greater ease of 
descent to and ascent from the arch- 
way would be attained, than by a sub- 
terraneously-excavated tunnel, which 
unavoidably-must pass at a consider- 
ably greater depth under the river. 
The other method is applicable 
wherever a crooked river winds round 
a low point of land, and consists in 
excavating on such point of land a 
portion of a new and straighter chan- 
nel for the river, but-leaving the ends 
thereof uncut, for excluding the river 
therefrom, until after the archway is 
completed across under such new 
channel, and thoroughly secured ; and 
then proceeding to eut out and dredge 
the two ends, so as to turn the river 
in an uninterrupted course over the 
archway ; and, when this is completed, 
forming an embankment across the old 
channel, and thereon constructing the 
road of approach from the opposite 
shore to the mouth of the archway. 
The inhabitants of Gloucestershire 
were a -fow years ago led to expect, 
that an archway-road would be formed 
across,under the Severn river, several 
miles below Gloucester, but which 
undertaking failed, after a consider- 
able sacrifice of property, in attempt- 
ing a tunnel; instead of which, if the 
low point of Jand, consisting of tena- 
vious clay strata below the Lias lime- 
stone, nearly Opposite to the intended 
en the Thanies. 
199 
tunnel, had been treated as’ above de- 
scribed, and as had then several years 
previously been’ recommended, the 
public might now have been enjoying 
the benefit of a new and important 
communication, and the undertakers 
receiving the just reward of their en- 
terprise ; at the same time that the 
navigation of the river might have 
been permanently improved by the 
alteration. 
I make these observations from no 
feeling of hostility towards Mr. Bru- 
nel; for whom, on the contrary, I 
entertain the highest respect: but from 
a desire to promote the accomplish- 
ment of the public improvement and 
accommodation to the inhabitants 
eastward of London which he contem- 
plates. 
Somewhat connected with this sub- 
ject, is the question now so keenly, 
and, I may add, so intemperately, 
agitated, as to the effects to be appre- 
hended on the wharfs and low lands 
near the Thames, which the pulling 
down o: Loudon-bridge, and substitu- 
ting one which shall offer little.or no 
impediment to the passagé of the tide, 
up or down: whereupon L beg to men- 
tion, that I entertain no apprehensions 
of mischief to arise from the removal 
of the present starlings, and unneces- 
sarily numerous piers, which so much 
obstruct the waters: but, on the con- 
trary, anticipate very great advantages 
from the proposed change. 
The tides all around our island, and 
on the opposite coast of the European 
continent, have, from some yet unas- 
certained cause, risen progressively 
higher during the last thirty or forty 
years, and perhaps much longer; and 
have, at short intervals, of late years 
occasioned much mischief on the 
banks of the Thames, even whilst 
London-bridge, with all its obstruc- 
tions, has been standing. If, as 1 
have conjectured, the cause of this 
increasing height of the spring-tides 
be connected in a chain of causes 
which as yet are mysterious, with the 
change of the magnetic variation, and 
the arrival of the same at its western 
maximum, which occurred in these 
parts in the spring of 1819, may we 
not hope, that now our tides have 
passed their maximum, and will de- 
crease in height, and so the chief 
cause of apprehension be removed: 
but, should my conjecture prove ill- 
founded, and the tides, not having yet 
reached 
