6 
The first consideration to which we must 
address ourselves in fixing the depth of drains, 
is the depth of soil required to be laid dry. 
There is a limit to the depth of drained soil 
required for the purposes of cultivation, and 
any extra expenditure in drying soil at greater 
depths than will yield a return, must be re- 
garded as waste. In England, cultivated plants 
seldom exceed two feet deep, but here, bananas 
and maize go considerably more, although how 
far I cannot say ; I presume that they go at least 
three feet deep in drained soil. The bottom of 
the drain should be from a foot to eighteen 
inches below the roots of the plants, so that 
they shall not be injured by the water upheld 
by capillary attraction. So then from four to 
five feet would be suitable for our climate, 
although it is considered that from three to four 
feet is suitable for England. 
[n porous soils, drains may be deeper and 
farther apart, because the water will readily 
flow to them from all parts, and the greater the 
depth the more powerfully will the capillary 
attraction of the soil be neutralized. In clay soils 
again, the drain has not only to carry away the 
water, but to aid in maintaining the artificial 
porosity of the soil, by means of which the 
water is to gain admission to it. This it cannot 
effect if placed at a depth to J which the shrink- 
age of the soil does not extend. The compara- 
tively slight benefit derived in many cases from 
drains in clay during the first season after their 
formation, more especially if it has been a wet 
one, is sufficient confirmation of this view. 
Frequency of the Drains . — The distances at 
which drains ought to be placed apart, is a sub- 
ject of great importance, and one on which 
much difference of opinion exists. Mr. Smith, 
(late of Deanston), who may be taken as the 
representative of one class of drainers, contends 
that the drains should be placed at very short 
intervals. He says — “In laying off the drains, the 
first object for consideration is, the nature of 
the soil. If it consists of a strong, stiff “ till,” 
or a dead sandy clay, then the distance from 
drain to drain should not exceed from ten to 
fifteen feet ; if of a ligher and more porous sub- 
soil, a distance of from eighteen to twenty-four 
feet will be close enough ; and if in very open 
sub-soils, forty feet distance may be sufficient.” 
On the other hand, Mr. Parkes, who represents 
the deep and distant drain system, says — “ It 
consists with my own practice at the present 
time, that drains are being executed at depths 
at from four to six feet, according to soil and 
outfall, and at distances varying from twenty- 
four to sixty-six feet ; complete efficiency being 
the end studied, and the proof of such efficiency 
being, that after a due period given for bringing 
about drainage action in soils unused to it, the 
water should not stand higher, or much higher, 
in a hole dug in the middle between a pair of 
drains, than the level of those drams.” 
The distance apart, like the depth of the 
drains, must be governed by a variety of cir- 
cumstances, all of which demand strict and 
careful investigation before proceeding to set off 
any system of drainage. The most important 
of these considerations is the nature of the sub- 
soil, and the effects which the removal of stag- 
nant water will produce upon it. In some soils 
a great degree of artificial porosity will be 
produced by draining; on these the drains may 
be further apart than on soils in which this 
cracking is less powerfully developed. 
The subsoils upon which draining acts to a 
shorter distance than perhaps any other, are 
those clay subsoils containing a larger quantity 
of imbedded stones. The great portion of their 
mass, which consists of inexpansible materials, 
prevents the production of that artificial porosity 
which plays such an important part in the drain- 
ing of the purer clays. 
A scale of distances varying from eighteen to 
forty feet, will be found to suit almost any case 
that may occur, while it will not incur the 
charge of waste of means on the one hand, or 
inefficiency on the other. In my garden at 
South Brisbane the drains are sixteen and a-half 
feet apart, and four feet deep : but from what I 
have seen of them they would act perfectly well 
were they twenty-four feet apart, and four and 
a-half feet deep. 
Then as to the direction of the drains, with 
reference to the declivity of the land. As the 
law of gravitation, when permitted to act by 
either natural or artificial porosity, is that which 
governs the descent of water into drains, so the 
chief object to be considered in laying out drains 
is to place them so that this principle will act 
most fully upon them. 
In flat land, all the parts of the surface will 
be in the same relative position as to height 
above the drain in it. The main consideration 
will be the place of discharge and the main 
drains. 
Where the slope or fall is very slight, the 
necessity for selecting the line in which it is 
greatest for the direction of the drains, in order 
to obtain a flow in them, will be admitted by 
all. This rule ought also to obtain in all cases 
of sloping land, no matter how steep the slope, 
because the line of the greatest fall is the only 
line in which a drain is relatively lower than 
the land on either side of it. 
As to the material of which the drain is made 
nothing can come into competition with pipe 
tiles. They are the cheapest in first cost, and 
if properly made, and have a fine ringing sound 
when struck, they may last for ages. Their 
cost in England varies according to the price of 
coal. Two inch pipes are quoted at 15s. per 
thousand feet, but the price of the same here is 
12s. per hundred feet, which is eight times 
dearer. The entire cost for making drains is 
quoted at 6£d. per rod for 31 feet deep drains. 
Another instance is given where the entire cost 
for labour was 51d. per rod, and this seems to 
be a fan* average for drains 31 feet deep. 
