280 Comparative Agriculture of England and Wales. 
regarding for a moment the superficial beds, we may say that the 
more extensive beds of clay carry . a large acreage of pasture, 
whilst the lighter or mixed soils have a preponderance of arable 
land. The Lias, Kimmeridge, and Oxford Clays are especially 
im()ortant. But through the greater part of the lower country 
north of the Thames and the estuary of the Severn, there is ?, wide- 
spread covering of Drift, which much obscures the main rock 
masses, and makes an ordinary Geological map almost useless 
for agricultural purposes. The stiffest clays are sometimes 
covered by thick and widespread sheets of gravel or sand, whilst 
the calcareous or sandy rocks may be covered by clay. Clay- 
drift over clay, or sand-drift over sand or liinestone, has a less 
striking, but often a not less important influence in modifying the 
agricultural features of a country. The distribution and cha- 
racter of these various drifts are as yet too imperfectly known to 
allow of a general description, and any attempt to describe the 
agricultural geology of a district, ignoring these where they exist, 
would be absurd. 
The importance of the drift-covering is nowhere more apparent 
than in the Eastern counties (Norfolk, Suffolk, and Essex) ; and 
there, too, the value of statistics in illustrating the distribution 
of crops is very well seen. The only striking physical feature 
of these counties is the Chalk hills, which, commencing on 
the Norfolk coast at Hunstanston, range south and south-west 
through their west and north-west borders. These hills attain 
heights of 600 and (j.lQ feet in West Norfolk. Their western 
face is steep, and in Norfolk the Gault, Lower Greensand, and 
Kimmeridge Clay crop out from below them on their western 
side. These beds do not appear at the surface in Suffolk, but 
underlie the Fen district at the north-western corner. In Essex 
they do not crop out at all. Chalk being the lowest bed of that 
county. The boundary line between the Chalk and the overlying 
Tertiary beds is obscured by Drift, but it ranges from Ipswich, by 
Sudbury, to Bishops Stortford, in Herts, just off the Essex boun- 
dary. The Lower Tertiary beds, where seen, are of no great 
thickness ; they are of most importance in the south of Essex, 
opposite Gravesend : here, too. Chalk reappears at the surface. 
The London Clay spreads over a wide area in Essex, where are 
also some small outlying patches of Bagshot Sands. The " Crag" 
appears on the east and south of Ipswich, and also to a smaller 
extent in Norfolk, chiefly near Norwich. 
The whole of these beds are very largely covered by drift, 
chiefly of two kinds : a clay containing many fragments of chalk 
(Boulder Clay), and sands or gravels. Both of these belong to the 
Glacial series of geologists ; but besides these there are deposits of 
gravel along the valleys, chiefly of the Thames and the Waveney. 
