Agricultural Notes on Hertfordshire. 307 
Immediately beneath the London, the Plastic clay crops out. 
The upper or clav-beds of this formation, as the name implies, 
are well suited for the manufacture of kiln-ware ; it is more 
tenacious, and less manageable than the London clay ; and usually 
forms a narrow band on the slopes and escarpments of the hill- 
sides ; the lower beds are of very pure sand, sometimes perfectly 
white, suited for domestic, horticultural, and other purposes, 
though some of the beds are interspersed with rolled pebbles. 
To the breaking up of this stratum much of the soil that covers 
the chalk is due, and from hence the hard conglomerate known as 
Hertfordshire pudding-stone is derived. The most fertile spots 
in this district arc found at the outcrop of these strata, where 
the clay and sand are amalgamated so as to form a friable and 
kindly soil. The geological condition here described extends 
more or less in a band across the county from Moor Park, near 
Rickmansworth, on the west, to its eastern limit bounded by the 
river Stort. 
The neighbourhood of Bishops Stortford furnishes a good 
example of farming under geological conditions not found else- 
where in this county, but resembling those which subsist in 
some parts of Essex. The river Stort runs through a trough in 
the chalk, over which the Plastic clay-formation crops out on the 
side of the valley. Its beds of clay and sand here amalgamate 
with the flint-gravel, with which the chalk is covered on the 
lower levels, to form a light, friable, and fertile soil, suited to 
four-course husbandry. On the higher levels the tertiary clay 
forms rather wide-spread " plateaus," covered very generally 
with a drift consisting of water-worn chalk, with some chalk- 
flints. This drift, for such it appears to be, is not found in the 
western parts of the clay-districts of Hertfordshire under the 
same geological conditions of subsoil, though it is very exten- 
sively diffused in Essex, where it presents some of the best corn- 
land in that county. It would be very interesting to trace the 
extent of this deposit in both counties, and, if possible, account 
for its unusual presence as a covering to the tertiary beds resting 
on the chalk. 
The Water-level in the Chalk, 
As in the case of the clays, the chalk-district may be sub- 
divided ; it has been so treated by Arthur Young, who, in his 
maps, lays down the principal part as loam, distinguishing as 
chalk only that small space which is drained by rivers running to 
the north with a fall anticlinal to the natural dip of the stratum. 
Adopting this division, of which it would be difficult to define 
the exact limits, we find that the southern slope from the 
northern limits of the county to the point where the river 
