Geolo()ical and A(jricultiiral Divisions. 
277 
rc(^uire lime, and as lime possesses the property of decomposing 
tHe silicates of the soil, and thereby assists in the production of 
the soluble salts which are indispensable to vegetable lile, it 
considerably abridges the necessity of fallowing. Almost all of 
the lower chalk is under the plough ; it makes very indifferent 
pasture when laid down to grass, unless it is irrigated by some of 
the streams which rise at the foot of the hills. It is very diffi- 
cult for a practical farmer, with only a limited knowledge of 
geology, to state whether there is any real development of the 
upper greensand in Bucks. An able geologist says, " the green- 
sand is a compound as incongruous as the great image with its 
head of gold and feet of miry clay. The gault is, in one place, 
lost in the upper greensand ; in another, the greensand is replaced 
by the gault ; and in a third, both appear to merge into the 
lower chalk." No wonder then that un-scientific persons can- 
not with certainty indicate its position and limits. There are 
certainly, in some parts of the county, beds of an argillo-calcareous 
character, and into these beds the lower chalk seems to graduate 
by an almost insensible transition. The change, however, pro- 
duces no marked diffei'ence in the character of the soil. 
On leaving the lower chalk, the gault is first found in situ at 
the bottom of Bledlow Field, and it stretches from thence, through 
Ilmer to Aston Sandford, forming a district two or three miles 
Avide. It then passes south of Aylesbury, and running by Win- 
grave enters Bedfordshire a little below Leighton. The gault 
clay is of a greenish-grey aspect, which grows darker in the 
atmosphere, and it is mostly a thin cold soil, which, when wet, is 
as sticky as glue. It is a most expensive soil to cultivate as 
arable land, and instances of this occur too frecjuently in Bucks, 
where perhaps is some of the stiffest ploughing in England. 
Some soils in the parishes of Cheddington and Weston Turville, 
and again in Walton Field near Aylesbury, are adhesive and 
stubborn to the last degree. Such land would always pay much 
better in grass ; and it is a happy feature of this part of the 
county that land will soon become a fair pasture, and even if 
laid down without any seeds, the natural grasses soon make their 
appearance. A rougli analysis was made of some soil taken from 
AValton Field, with a view only of ascertaining the amount of clay 
which it contained. After being dried, the result showed 26 per 
cent, of impalpable clayey matter, and 58 of silica ; the remaining 
16 per cent, being composed of lime, iron, potash, &c. This 
shows what a very strong soil it is, for the proportion of alumina 
in the purest pipeclay rarely exceeds 36 per cent. 
The iron or lower greensand enters Buckinghamshire on the 
north-east at Bow Brickhill, and from thence to Leighton Tunnel, 
