176 
Causes of Fertility or Barrenness of Soils. 
out of ditches, and corners of fields, present excellent material 
lor the purpose. 
Tiie principal clay districts in this country are those of the 
London and Plastic l)eds, occurring in the south-eastern counties ; 
the Wealden, found in parts of Surrey, Sussex, and Kent ; the 
Lias, forming a narrow band, which runs from S.W. to N.E. 
right through the country from the Vale of Gloucester to York- 
shire ; the clays of the Old Red Sandstone, occurring in Devon- 
shire ; and the clays of the older rocks, developed principally in 
Wales. Besides the above a number of smaller beds occur, as 
clay is found in almost every formation ; indeed, very few soils 
are devoid of some portion. We have hitherto spoken of those 
soils which contain a large proportion of clay ; the most fertile 
districts contain clay mixed with certain proportions of sand, known 
as clay or sandy loams. The value of such soils consists in their 
containing sufficient absorbing and retentive power for vegetation, 
at the same time being open and to some extent porous : in fact, 
Nature has in these cases prepared the soil and saved much of the 
labour necessary to the stiffer clays. When resting on a porous 
subsoil, clay loams do not require draining. In other cases it is 
only necessary to remove the superabundant moisture in order to 
have a soil in every way fitted for the wants of plants. Such soils 
turn up as a fine mould, into which the atmosphere has ready 
access, and the roots can throw out without impediment. Clay 
loams should be looked upon as the standard to which by energy 
and capital we are to bring the stiffer beds ; and though in the 
absence of sand it is vain to hope for the permeable and mouldy 
character, yet it is astonishing what alterations the strongest soils 
are capable of under judicious management. The addition of sand 
to clay w ould be very beneficial, but the great quantity required to 
make any alteration unfortunately prevents this being carried out. 
Silicious or Sandy Soils. — This term is applied to all soils 
principally composed of silicious matter, either in the form of 
fine sand or of coarser sand and gravel. They possess qualities 
the very opposite of the last class, being light in colour, varying 
from a white silver sand to a rich red, exceedingly porous. In 
reality heavier than clays, they appear light from the absence of 
all cohesiveness. They neither attract gaseous matters from the 
atmosphere nor retain the manures put into them ; hence the 
poorer and purer descriptions are known as hungry soils, and 
are barren and unprofitable to cultivate. Not retaining moisture 
and being so permeable, these soils are warm ; the heat, too often 
rendered latent by evaporation in a wet soil, is enabled to pene- 
trate and warm every portion, rendering them peculiarly suitable 
for rapid germination ; the seed never lies long in the ground, 
provided there is sufficient moisture. I have known swedes, 
