294 
Variationss of the Four-course System. 
In favourable situations they rarely fail to yield heavy crops 
both of roots and of cereals. 
5. Clayey soils, containing upwards of 70 per cent, of clay. 
These soils have been much improved by draining, though in 
many cases not to the extent which a large expenditure would 
have j ustified us in anticipating. Many of the leading drainers 
of forty or fifty years ago were led astray by the erroneous idea 
that, even on the strongest clays, depth was equivalent to dis- 
tance apart. Much of the deep draining on this class of soils 
has proved inadequate. Nevertheless, where the work was well 
done the land has immensely improved, and even the tillage 
land has assumed new characteristics. 
Where a good system of cultivation has been carried out, the 
laud suitably manured at stated intervals, and worked in a 
moderately dry state, the strongest soils have given way to the 
ameliorating agencies, frost and water, and have become more 
friable and more easily moved. In former years the four- 
course system was undoubtedly the means of improving agri- 
culture over a large extent of the British Isles. The discovery 
and use of guano and of other artificial fertilisers gave an im- 
petus to the cultivation of roots, the extended production of which 
necessitated on all farms an increased head of stock in order to 
consume them, and as a result a greater quantity of manure was 
made, ddie use of cereals for fattening became general, and was 
subsequently supplemented by linseed and other cake, as a result 
of which the land and crops began to show a marked improve- 
ment. T'he fame of the four-course system was wafted to distant 
lands, and it frequently gained a footing on strong adhesive clays. 
So arbitrary and uncompromising a system was, however, in 
advance of the general knowledge of the tillers of the soil, and 
hence arose disappointments. It was found that the adhesive 
clays could not, in dry climates, be reduced to a sufficiently fine 
tilth in time to receive the seed. Even if the seeds did vegetate 
their progress was slow, and the young crop readily fell a prey to 
the turnip fly or other pests. In favourable seasons, when the 
crop escaped these disasters, if a showery autumn set in the roots 
could in no case be fed off on the ground, whilst the land was 
much poached and injured by haidiug off. 
The four-coui’se system, with its unvarying cropping, had 
long since begun to tell unfavourably on the produce of the soil. 
A quarter of a century ago, on the best-managed farms cultivated 
under this system, twenty to twenty-five loads of farmyard 
manure was considered the regulation dressing for the turnip 
crop. This manure was for the most part made in open yards 
