422 
Oil D mild III/. 
and not at the surface, clay is a better material than mixed soil. 
Where drains arc jHled-in with mixed soil, injury is likely to 
accrue to the conduit by the soil running down and choking it, 
and particularly so if the conduit is formed with wood or straw, 
when it decays. If the mixed soil does not run into the conduit, 
but concretes, it vvill be more impervious to the entry of water 
than clay, as mixed soils contract much less than clay from the 
action of the atmosphere and operation of under-drains. 
I have repeatedly observed in heavy rains (on land imperfectly 
drained) the water running to the lower end of the field, and 
overflowing the lands almost to the ridges ; the greater quaidUij 
will ■percolate rayidly throuc/li the tilth and Jissiires to tlie conduit 
of the drain ; but the smaller quantity, when it is reduced to the 
furrow, and has to fdter through the deposit of mud and Jillinf/- 
in, will be days in disappearing, unless aided by drying winds 
or frost, which, by contracting the surlace-soil, admits the water 
into the fissures of the subsoil. With drying winds part of the 
water is evaporated, but by frost it is the contraction of the soil 
only which facilitates its infiltration, so that water will disap- 
pear in one night which would otherwise lie for days. 
In this county (Huntingdonshire) for the last sixty or seventy 
years furrow-draining has been practised ; and for the last ton 
years I think to a greater extent than in any district in England. 
Before the reduced price of draining-tiles, a system of block- 
chaining on very stiff soils was practised; a drain was cut from 
20 to 30 inches deep, 2 to 3 inches wide at the bottom, in which 
a round or other shaped block 3 feet long, or two or three shwrt 
blocks connected together, of the same length and of the diameter 
of the bottom of the drain, were used. The firmest clay thrown 
upon the block or blocks, and with a rammer beaten upon the 
same ; the block or blocks were then drawn forward by a lever 
or small capstan 2 or 3 feet, and the operation repeated in this 
manner throughout the whole length of the drain. The per- 
inancncjj and icorkiiifj of drains formed in this manner depended 
npon the drain heiny deep, and, the pure clay being firmly beaten 
doiori upon tlie wooden block or blocks, and making the conduit appa- 
rently impervious to the admission of tlie water. 
When this work has been carried on during the winter, and 
the atmosphere could have very little influence in contracting the 
clay round the conduit, to re-open the fissures closed by the ope- 
ration of the rammer in beating the clay on the block or blocks, 
still there was no complaint of the water not entering the conduit. 
In this mode of draining the water must enter on a level with the 
bottom, for if the work is well done it cannot percolate through 
the arch until by the atmosphere fissures are formed in it. 
Where land is drained by the mole-plough, the spear or mole 
