222 On Manures. 



grass, causes a fermentation and putrefaction, which seem ne- 

 cessary to produce a full effect. 



The quantity of clay or red marl used, is enormous, in 

 many cases about 300 middling cart-loads per acre ; and the 

 fields are sometimes so thickly covered, as to have the appear- 

 ance of a red-soiled fallow, fresh ploughed. In some cases, 

 slighter coverings are preferred, and the process is more fre- 

 quently repeated. It is proper however to remark, that much 

 injury has been sustained, from over-dressing with clay and 

 marl, without making at the same time, an adequate application 

 of rotten turf, sheep droppings, farm-yard manure, or some 

 other enriching stimulant. The application of clay and marl, 

 should always be regulated by the quantity of manure that 

 can be spared. A heavy coat of cold clay, or marl, without 

 dung, upon land poverty-struck by injudicious tillage, is so 

 extremely injurious, that it cannot be too loudly reprobated. 



Marl, after carting, is left oil the ground in a rough lumpy 

 form, that it may be exposed as much as possible to the in- 

 fluence of the weather. It should partake of one summer's 

 sun, and of one winter's frost, by which it is reduced into the 

 form of an unctuous, but friable material, the further disper- 

 sion of which, is easily effected, by clodding beetles, or mal- 

 lets, spades and harrows. It is thus equally distributed over 

 every part of the surface, and afterwards ploughed in ; and 

 the effects are represented to be in the highest degree bene- 

 ficial ( z * z ). 



In regard to shell-marl, it consists chiefly of calcareous mat- 

 ter, the broken, and partially decayed shells of fresh-water 

 animals, found at the bottom of lakes and ponds, often covered 

 with mud. It may be applied as a top -dressing to wheat and 

 other crops, when it would be hazardous to use quick-lime. 

 In the counties of Selkirk, Forfar, Ross, Caithness, and in 

 other districts, shell-marl has been of great value in fertilizing 

 the soil, though, from its stimulating powers, the land has been 

 often injured, by employing it in too great quantities, and 

 afterwards injudiciously over-cropping. 



6. Sea Shells. This manure abounds in various parts of the 

 British Isles. When pure, it is superior to the usual sorts of 

 limestone, in respect to its proportion of calcareous matter. 

 It likewise often contains a small portion of animal substances. 

 These shells have not, however, unless when burnt, the same 

 rapid and powerful influence on the soil. When not burnt, 

 they are much improved in their effects, if broken by a mill 

 resembling that used for tanners' bark, to give the air a readier 

 access to promote their decomposition, and to enable them to 



