576 
Abstract Report of Agricultural Discussions. 
consequences will swell into large dimensions, and will render the- 
object one of the most difficult and important engineering problems 
ever presented for solution. 
Although the soils of Great Britain alternate so frequently, and are 
so much intermixed, it is still possible to classify them, so as to 
render intelligible the statement that the frequent parallel system 
applicable to one description of land is inapplicable to the other. All 
soils having a proportion of alumina greater than 15 per cent, may 
be termed clay soils, and require frequent parallel drains to overcome 
their peculiar retentive character. These soils cannot be aerated too 
much, as it is only by aeration that their retentive nature can be 
overcome, and their bulk rendered permeable. Soils with a less pro- 
portion than 15 per cent, of alumina admit of percolation, more rapid 
as the proportion becomes less, and the retentiveness, which arrests 
the water in the clay, is diminished. Aeration is not necessary for 
di'ainage in wet soils altogether devoid of clay, and they are therefore 
called " free soils." Whereas, in dense clays, you cannot put in too 
many drains, it is the ne plus ultra of drainage of free soils to reduce 
to a minimum the number of under-conduits by which to relieve the 
land of stagnant water. Test-holes decide the number with accuracy ; 
and, wherever test-holes are the guide of operations, parallelism is the 
exception, and not the rule. 
It is found practically, that the clay lands cannot be drained by . 
means of test-holes. The expansive character of the soil, and the 
action of the atmosphere upon the sides of the test-hole, do not admit 
of the water passing from the test-holes to the drains with that ready 
response to the rainfall which is to be observed in free and mixed 
soils ; and the recognition of this fact will confirm the classification 
of wet soils, by distinguishing the soils that can be drained by test- 
holes, and which reject uniformity of design, from those which cannot 
be drained by test-holes, and which require that complete aeration 
which is only to be gained by the reciprocal influence of one drain 
upon another. It is a common observation with the cultivators of 
heavy lands, that it is not possible to get rid of water too fast ; and, 
in clays, this is found to be true, if tbe convenience of cultivation, as 
at present conducted, is alone considered ; but, since to get rid of 
water with rapidity from high ground is to cause injury to the valleys 
below, there is some consolation to be derived from the gradual 
j)rogress of steam and deep cultivation, inasmuch as the effect of deep 
gtirring is to render fewer drains necessary to produce the required 
effect. 
This observation, however, is altogether erroneous when applied to 
the free soils. All that is there necessary, under any conditions, 
is to set the water in motion ; and the fewer the number of drains that 
will effect this object, the more perfect the drainage, and the better 
the natural powers of the soil are developed. The effect on the 
arterial system is explained by the fact that, in proportion to the 
number of drains in all soils, but in free soils particularly, will be 
the rapidity of the discharge, and, necessarily, the augmentation of 
floods below. The fact is distinctly shown by the Hinxworth cxpcri- 
