414 
0)1 Draining. 
in the furrow over the drain, I found that the infiltration of the 
water into the drains was not iinj)eded by what the drain was 
filled with immediately above the tUes, or odier material of which 
the conduit was formed, but by the deposit of mud on the bottom 
and sides of the furrow carried there by the water running over 
the surface of the land, an<l from the bottom of the furrow at a 
higher level than where the water lay. The truth of this I 
proved by the following means : — After the water had remained 
till it was clear, and not higher than the floor upcni which the tilth 
lay, I have had the water taken out, and carefully removing only 
3 or 4 inches of earth from the bottom of the furrow, watch- 
ing that the spade should not smooth the floor, nor the operator 
set his feet upon it, poured the water back again, when it has dis- 
ajjpeared in two or three hours. I have also, under the same cir- 
cumstances, cut a channel 1 foot, sometimes 2 feet, from the furrow 
(where the drain was immediately under it), parallel to the 
furrow of the same depth and surface, and then allowing the 
water to pass slowly into it, in two or three hours the water has 
disappeared which would otherwise have lain for days. I have 
in some instances, even where water was lying on the surface, 
found at a foot deep the common earth-worm at work, which 
also proves that the water was prevented by the sediment de- 
posited on the bottom of the furrow from entering the land, as 
the worm cannot live in water. These experiments prove that 
the drainage of tenacious clay soils cannot be perfect if the water 
has to enter the drain from the surface, or through tlie jilliuf/-i)i 
immediately over it — for at whatever depth the drain may be laid, 
or the materials used to Jill in above the conduit, there must be, 
for the acts of cultivation, 8 or 10 inches of soil of the same 
nature as that of the field, and if that be of a tenacious nature, 
the drainage will be imperfect, from the facts before stated. 
The truth of these observations is exemplified in the drainage 
of pasture land — if two fields, one pasture, the other arable, are 
drauied shallow, and in every way the same ; if the land be un- 
dulating, the water, after a continuation of wet weather, will lie to 
a much greater extent upon the flat parts of the arable field than 
upon the pasture land ; although the surface of the arable land 
may have been recently moved by the plough ; the reason for 
which is that the water, in running over the surface and furrows 
of the grass land, does not become thick and turbid as upon the 
arable, consequently there is not the deposit to prevent that part 
of the water which is not carried to the drains by infiltration 
through the fissures, from filtering through tlie Jilling-in above 
the conduit. 
In land drained by open drains, very much the same effect is 
produced according to their depth as by under-drains ; thus with 
