246 On the Agricultural Geology of the Weald. 
tte bulk of the soil, so that roots can penetrate to a greater depth, 
in good soil, than Avithout them.* 
Not much of the Kentish Chalk is unenclosed, but very large 
areas of the Sussex Chalk are in open " Downs." This difference 
is owing to the greater quantity of superficial covering in Kent 
than in Sussex. Mushrooms grow in great quantities on the 
Sussex Downs, and it is on record that the produce of a field of 
11 acres sold one summer for 25/.t 
Upper Greensand. 
On the coast at Folkestone this formation is seen to consist of a 
greenish sand, calcareous or clayey as it approaches the Chalk 
above or the Gault below. Its thickness is about 20 feet, but 
inland it rapidly thins away in a mile or two, and is represented 
only by some green grains at the base of the chalk. There are 
no hard beds of firestone at Folkestone. 
In Surrey the Upper Greensand becomes important, and forms 
a well-marked terrace at the foot of the Chalk escarpment ; and 
from thence, all round the Weald, to the coast at Eastbourne, it 
has the same general characters. 
In Surrey it consists of three divisions : — At the top, just below 
the lowest marly chalk, is a greenish marly sand with phosphatic 
nodules ; below this comes a siliceous rock of various degrees of 
hardness and thickness ; the harder beds are known as " fire- 
stone." It is this division which yields a high percentage of 
soluble silica. Sometimes there are hard beds of blue lime- 
stone, which are quarried for building stone. Below this is a 
greyish marl or clay, resting upon and passing into the blue 
clay of the Gault, with which, perhaps, it might be classed, for 
there is no strong natural line between Upper Greensand and 
Gault. 
The divisions of the Upper Greensand, as they exist near 
Farnham, have been already described in this Journal by 
Messrs. Way and Paine.J The silica which occurs in a soluble 
* "So thick is the fliut-drift, spread like a coverlet on a bed of chalk, in some 
of the dry hollows, that cultivation -would seem as little profitable ther6 as on the 
shingle of a sea-beach. But you are re-assured when told of the costly experience 
of a new-comer, who, having picked off the flints and carted them away, and 
thereby lost his crops, acknowledged his error by restoring them, as shelter 
against March winds, protection against summer suns, and warmth against winter 
frosts." — DicJicnson's Farming of Hami^shire ('Journ. Eoy. Agr. Sot.,' vol. xxii., 
p. 253). 
t M. A. Lower. " The South Downs." ' Contributions to Literature,' p. 154. 
X ' On the Silica Strata of the Lower Chalk,' vol. xiv., p. 225. This, and two 
other papers in the Society's Journal by the same authors, must be read by all 
■who would study the Agricultural Geology of the Upper Cretaceous Beds ; parti- 
cularly those of the neighbourhood of Farnham. (See ' On the Phosphoric Strata 
