CCHVL MEASURES IN THE SOUTH-EAST OF ENGLAND. 
229 
and lie estimates the thickness of the whole at Oxford at about 
600 ft. ; whereas in Gloucestershire it is 1,880 ft. : — 
Gloucestershire. Oxford. 
Feet. Feet. 
Great Oolite and Fullers Earth . 
. 370 . 
. 205 
Inferior Oolite and Sands . 
. 420 . 
0 
Lias (Upper and Marlstone) 
. 640 . 
. 200? 
lied Sandstone and Marls (Keuper) 
. 450 . 
. 200? 
1,880 
605 
To the north-eastward the Great Oolite and the Oxford Clay 
become but slightly thinner. On the other hand, the Kim- 
meridge clay, which is 275 ft. thick at Swindon, is 310 ft. near 
Abingdon, and increases to 450 ft. at Aylesbury. In like 
manner, the Portland and Purbeck series increase from 12 to 
70ft. ; while the Wealden series, which is altogether absent in 
the west of England, is about 2,000 ft. thick in Surrey and 
Sussex. So the Lower Greensand, which is only 50 ft. near 
Devizes, attains a thickness of about 500 ft. at Eeigate. The 
Gault maintains a mean thickness of about 100 ft. ; while the 
Upper Greensand, 150 ft. thick at Devizes, is reduced to 25ft. 
at Merstham. The Chalk, taken at its full development, main- 
tains tolerably constant dimensions from Wiltshire to Dover, 
viz. of from 800 to 1,000 ft. unless when, as often happens, it 
has suffered denudation. Notwithstanding, therefore, the large 
development of the Secondary formations, both westward and 
northward of the London basin, it was uncertain how many 
and how much of these might be found to extend under the 
Tertiary strata of the south-east of England. We did not 
anticipate, however, the great hiatus which in reality has been 
found to exist. Whatever might be the case with the triassic 
and jurassic series, it seemed at all events probable that the 
lower cretaceous strata, which are so fully developed a few 
miles both on the north and south of London, would, like the 
upper cretaceous strata (the chalk), pass under London, and 
therefore it was a matter of surprise when the boring at 
Kentish Town, made in 1854, showed that not only were the 
older secondary strata all absent, but also the lower greensands, 
which are so well developed in adjoining parts of Kent and 
Buckinghamshire. In the place of the latter were found a 
series of red and grey sandstones belonging probably to the 
Old Ked Sandstone, so that the following diagram (fig. 2) may 
now be considered as representing probably the order of suc- 
cession and position of the strata from the West of England to 
London 
In the same way MM. Dufresnoy and Elie de Beaumont* 
* “ Explication de la Carte Geologique de la France, 1841,” vol. i. p. 727. 
