132 
preserved. Dr. Mitchell gives the following list of the total depth 
of wells, selected from a very large number: 
Dtratlordyas Cnet ce Meee nce 247 feet. 
LINCO a itl ee aM ls csi nla 301 — 
Wasniam rallye nee Ns eee s 4045 — 
IBTOOK-Strecb Utena cele ste cree aes 340 — 
Upminster yo veee seers eat 192 — 
iParsonage;“Warley .f.- ts mer ee 390 — 
Grange Hill, near Fairlop .......... 398 — 
HTD un Gan Te AS tre ea 344. — 
Battle:Bridgest::...2. 2 oe 390 — 
Ferry-house on the Crouch.......... 360 — 
Rochford Union workhouse............... 3830 — 
Wraikernnoe Marshes vio a) seiner 400 — 
Foulness Island sie Meaney a on 460 — 
clay, 100 to 160 
Clay-street, Walthamstow ...... eoee 190 — 
Loughton, in Epping Forest ........ 324 — 
Rppine yy ev cee i. . Sak Seka 270 — 
Horsley Park, near Ongar.......... 340 — 
OCI tt Se entnna ee aan ns. ere 370 — 
BTAIMtTeeH es paeetenom etn vars ae tee) Mees 
This variation the author conceives, is partly due to the uneven- 
ness in the surface of the chalk; but in some instances to the un- 
dulatory nature of the country, the difference in the depth of the 
wells agreeing with the increase in the rise of the ground. When 
this is the case, the bed in which the water is found is the same in 
the adjacent wells, and consequently the variation in the outline of 
the surface is due to denudation, and not to unequal elevation. 
Thus, in the two wells close to the turnpike at Romford, water was 
found at the depth of 100 feet, but half-way up the hill between 
Hare-street and Havering Ate Bower at the depth of 250 feet; at 
Bocking it was obtained at 370, but at higher ground, at Braintree, 
close adjoining, at420. Again, at the union workhouse in Rochford, 
the well is 330 feet deep, and at Stroud Green, on the road to Rug- 
leigh, where the surface is higher, it was necessary to sink 390 feet. - 
At North Fambridge is a well 388 feet deep, the water rising to 
within 10 feet of the top: but at another well in the same parish, 
dug in lower ground, there is a constantly flowing stream. 
In the New River Company’s well at the end of Tottenham Court 
Road, chalk was found at the depth of 150 feet; but in that near 
Pond-street, at Hampstead, the main spring in the bed of sand 
between the London clay and the chalk, was 330 feet from the 
surface. 
The London clay in Essex varies greatly in colour, being in some 
places yellow or red in the lower part, but in many localities it is 
blue to the bottom. It is sometimes uniform in composition through- 
out, but more frequently, even when only 100 feet in depth, divided 
into two or three portions by beds of sand. In the well at the site 
