4 
that although it seems saturated with water in 
all its parts, yet that the quantity of water 
which produces saturation in the higher parts 
is less than that in the parts next the table. 
When rain falls upon the surface of soils, 
'which rest upon an impervious, or very slightly 
pervious substratum, it is gradi.ally diffused 
through all the porous and absorbant portions 
by capillary attraction, assisted in clays by the 
cracks and fissures they contain. If the fall 
continues the soil becomes saturated, and the 
excess then forms pools, or makes its escape by 
flowing over the surface to any neighbouring 
water course. 
When the rain ceases to fall those parts of 
the surface which are higher than the rest 
gradually become drier, because the water be- 
ing no longer upon them the la w of gravitation 
produces its natural results. Now, we cannot 
raise the soil, but we can, as we shall presently 
see, lower the impervious or saturated bed on 
which it rests, and so increase the depth of the 
porous soil. 
If we cut a drain or trench into the subsoil 
we immediately disarrange the hydrostatic rela- 
tions which exist in the neighbourhood in a 
greater or less degree according to the depth. 
The capillary force which retained the water in 
the soil to the height of a few inches, is no 
longer able to sustain it when the height is in- 
creased to feet ; so a portion descends into the 
drain, leaving the upper part of the surface 
comparatively dry. Now the unequal pressure 
of different heights of water in the land, im- 
mediately compels the portion of soil next to 
that from which the water has been drawn to 
yield up a portion of its excess to it, obtaining 
in its turn a portion from that farther off, and 
bo on through the whole mass of the surface soil ; 
but as faBt as it is supplied the drain draws it off, 
bo that in a short time the level of the water in 
the whole mass is lowered. This is the action 
■which is indicated by the term drawing which 
is so often applied to drains. 
All soils too, but especially those containing 
clay, possess the property of expanding when 
wetted, and contracting when dried ; so that 
after the drain has removed a portion of the 
water a considerable contraction takes place. 
But this is especially noticeable in a dry season. 
As the ends of a field cannot approach each other 
to suit the contraction, both soil and subsoil are 
torn asunder and divided into small portions by 
a network of cracks and fissures. 
These phenomena are of the utmost conse- 
quence in draining land ; indeed it may w ell be 
doubted, whether without such properties in 
the soil or subsoil, we could drain our clay 
lands at all. It is worthy of remark here, that 
as on stiff soils the cracking action is strongest, 
nature seemed to second the efforts of man, 
and compensates the want of porosity in clays 
by the more powerful development of a pro- 
perty which under skilful treatment renders 
them almost as easy to drain as the more porous 
soils. 
The tendency of draining is to increase and 
guide the course of this cracking action. The 
main fissures all commence at the drain and 
spread it from in almost straight lines into 
the subsoil, forming so many minor drains 
or feeders all leading to the conduit. These 
main fissures have numerous small ones diverg- 
ing from them, so that the whole mass of 
earth is divided and subdivided into the most 
minute portions. The main fissures are at first 
small, but gradually enlarges as the dryness in- 
creases, and at the same time lengthen out, so 
that when a dry season happens they may be 
traced the whole way between the drains. 
When the fissures are once formed, the falling 
of loose earth into them, the roots of plants 
penetrating them, and the grooving action of 
the water which passes through them, prevents 
them from ever closing so perfectly as to hinder 
the passage of water ; while each successive sum- 
mer produces new fissures, till the whole body 
of the subsoil is pervaded by a perfect network 
of them, which gradually alters the very nature 
of both soil and subsoil ; and in connection 
with judicious and liberal manuring has the 
effect of converting poor cold clays into some- 
thing not very different from a good clay loam. 
Of the depth of covered drains for drying the 
land through which they pass. — Such drains 
have a twofold office to perform. They have to 
to collect the water from the soil, and then to 
carry it off in a certain fixed course. They 
must therefore afford free access to the water at 
all points and at the same time, and prevent it 
from leaving them by any other way than by 
their own channels. 
Modern agriculture has shown, that to have 
large crops we must have a deep soil. The soil 
is the great storehouse of the materials of which 
plants are composed, but these require a certain 
i amount of preparation before they become 
! fitting food for our crops. That preparation is 
! effected by exposing them to the action of the 
elements through the operations of tillage. 
Plants have the peculiar property of being able 
to adapt themselves to almost any amount of 
food which may be presented to them. Take 
turnips for example ; these will be found vary- 
ing from the size of a pigeon’s egg to that of a 
! man’s head, or even larger, according to the 
amount of food with which they have been 
supplied. It is therefore an object of the first 
importance that a large quantity of what 
; chemists call the “inorganic” constituents of 
; plants be constantly in course of preparation in 
! a soil deeply stirred by the sub-soiler or trench- 
plough. Drains then must be put in so as not 
to be disturbed by the operations of sub-soiling, 
and that would require a depth of about thirty 
inches. 
But the preservation of the structure of the 
drain is not the only thing to be considered ; 
there is the equally important and far more 
difficult question : What should be the depth of 
drains in reference to the results required of 
them ? 
