Geology of England and Wales. 145 
Chichester to Worthing. The country is generally low, or only 
slightly undulated, and as a soil it is productive of fine oak, 
elm, and ash timber, but requires chalk to render it productive 
in corn; when well manured it forms excellent garden ground, 
as the vicinity of London amply testifies. 
The history of the wells in London, is very interesting, as 
connected with the clay formation, and they may be divided 
into three classes. 1. Those which are in the gravel above the 
clay. 2. Those in the clay itself. 3. Those which derive their 
supply from the strata below the clay. A great deal of good 
limpid water is derived from the first class, where its escape is 
prevented by the dense nature of the substratum. Sometimes 
it is rather hard, and sometimes brackish, but generally speak- 
ing very good drinking water. This supply, however, though 
abundant, is generally insufficient for the consumption of our 
ereat manufactories; yet some of the large sugar-houses, dis- 
tilleries, and breweries, exclusively employ the water of these 
shallow wells, which in some parts of the town are remarkably 
productive. 
Where the diluvial gravel is very thin, or altogether wanting, 
there are wells sunk in the blue clay, but the water is extremely 
impure. Selenite is its common ingredient, and sometimes the 
pump delivers nearly a saturated solution of that salt. Sul- 
phate of magnesia, sulphate of soda, sulphate of iron, and occa- 
sionally sulphuretted hydrogen, are also found in the waters 
from the blue clay. The supply of these wells is very pre- 
carious, and, literally speaking, very scanty; for they generally 
receive the drippings of the thin superincumbent diluvium. 
The third class of London wells includes those which per- 
forate the clay, and derive their water from the strata beneath 
it; these have lately become very numerous, and are truly 
important in many of our large manufactories which were before 
obliged to employ the muddy water of the Thames, or to submit 
to the capricious supplies and wanton impositions of the Water- 
Companies. The water which supplies these wells rises from 
the sands below the London clay; andif care be taken to exclude 
the impure springs which filter in from above, it is generally 
remarkably soft, excellently adapted for every domestic use, 
and, what is of principal importance, it never fails, and is not 
affected by rains or drought: traces of common salt and of carbo- 
nate of lime, are usually discoverable in it, but what is most re- 
markable is, that when evaporated it leaves a highly alkaline 
residue, chiefly of carbonate of soda, which sometimes amounts 
to four grains from the quart. The depth of these wells is, of 
course, dependant upon the thickness of the clay stratum. At 
White-Chapel, east of London, some wells have been carried 
through it, and do not exceed 100 feet; at Tottenham it is 
about 120 feet; at Messrs. Coutts and Co.’s banking-house in 
