Causes of Fertility or Barrenness of Soils. 
181 
field, and thus increase the productiveness of liis land. Occa- 
sional draininj? may become necessary from the presence of a 
vein of clay between two porous beds ; but this is generally a 
simple operation, as we can often empty the drain into the porous 
rock, without any fear of tlie waters reappearing. There are 
other considerable limestone soils, such as the mountain limestone, 
and many smaller tracts scattered over all parts of the country. 
The presence of a small proportion of lime is indispensable to 
every fertile soil, and as the quantity required is small, it forms 
a most important application to all soils tliat are deficient in this 
respect ; it is used either as a carbonate in the form of chalk, 
limestone, &c., or in the caustic state, as quick lime. The opei'a- 
tion of lime under the latter form will be best discussed when 
describing the chemical peculiarities of soils. 
Peaty or Vegetable Soils are those in which decayed vegetable 
matter, or humus, forms the principal ingredient, or at least gives 
distinctive character. They vary very much (according to the 
quantify of humus, and absence or presence of other bodies), from 
the rich vegetable soils of the garden to the peat bog, which is 
often valueless until earthy matters, as clay, sand, or lime, are 
added. These soils are dark in colour, light and spongy in 
texture, and, though deficient in cohesive properties, powerful 
absorbents, and generally resting upon clay, require drainage before 
they can be cultivated. Peat also possesses a considerable reten- 
tive power itself, due to the undecayed cells of the vegetable 
matter, which retain and allow of the moisture rising to the surface 
by capillary attraction. Peat beds have in most cases resulted 
from the gradual decay of mosses, &c., under water until the 
continued growth and decay has reached the surface, when the 
whole mass assumed a semifluid state ; the peat is not, therefore, 
generally very deep. When practicable, it is important to lay 
the drain in the substratum, as aft'ording a sounder bottom and a 
better material for the pipes to lie in, as well as arresting the 
moisture before it can rise in the peat. The physical character 
of peaty soils varies considerably, depending upon the amount of 
decay they have undergone : when first brought under cultivation 
they are very open and cellular in structure, becoming finer and 
more mould-like by exposure to the atmosphere. The deposit of 
peat being very partial, the soils are limited in extent, the prin- 
cipal tracts existing in parts of Ireland, and in Lincolnshire and 
Bedfordshire, forming the Great Bedford Level. 
riie hasty glance we have thus taken of the principal classes 
into which soils may be divided will assist us in determining the 
importance of the physical properties they possess. The dis- 
tinctive character of clay soils is their tenacity, dependent on the 
power of absorbing and retaining moisture. The relative power 
of various soils to absorb moisture was determined by Sir H, 
