114 A PRACTICAL TREATISE 



second and further applications have been successful; the 

 reason of which evidently is, that, in the first instance, the 

 fertility of the mould was either exhausted by the chemical 

 effect of the marl, or, that, the soil being- of a heavy kind, and 

 the marl containing- too great a proportion of clay, tiiis addition 

 became injurious; while, in the second, dung had been applied 

 in aid of the marl, or, its earthy properties being- of a nature 

 opposed to those of the soil, assisted in its amelioration. The 

 latter of which suppositions is, indeed, supported by the fact, 

 that wlien a second application of clay-marl has failed, lime 

 has been laid upon the same land with sensibly good efl'ects. 



It has also been observed, in those places where marl is 

 applied to the land in small quantities at stated distances of 

 time, and where a sufficiency of dung is likewise used, that 

 when weeds of any peculiar species push forward with extra- 

 ordinary vigour, marl, if accompanied by a clean fallow, not 

 only de'stroys them, but produces better corn than when dung 

 has been laid on alone, though also upon a fallow, and instead 

 of marl ; which has been thought to be accounted for by the 

 exuberance of the weeds proving that the soil is already abun- 

 dantly furnished with nutritive matter for the promotion of 

 vegetation, but that it is more appropriate to the production 

 of the weed with which the ground is covered, than to cereal 

 crops: whence it has been inferred, that the chemical action 

 of the marl probably changes the nature of the mould. 



The durability of the effects of marl necessarily depends 

 upon its power over the soil. A very large dose of argilla- 

 ceous, or clayey marl, ameliorates sandy soils to such a sensi- 

 ble degree by the consistence which it affords to the land, 

 that, if proper attention be paid to its complete combination 

 with the surface, and to the prevention by careful culture of 

 its sinking to the subsoil, as well as to the employment of pu- 

 trescent manure, the improvement thus effected will be found 

 permanent. When laid on in smaller quantities, its effect 

 and duration will, on those light soils, of course, be proportion- 

 ate; but on clays, as its chief power consists in the calcareous 

 matter which it contains, its greatest effect is apparent when 

 the land is brought into the second course of tillage, after 

 which it gradually begins to decline, and afler six or eight 

 crops have been grown, it usually ceases to operate. 



