VEGETABLE MANURES. 



HU 



and ill some districts, the calcareous matt^ir is mixed with an 

 adhesive clay {day-marls). 



252. The followino- is the composition of some specimens 

 of marls, examined in my laboratory. In 100 parts, they 

 contain respectively as follows: — 



IJesides therefore conveying to the soil, when applied as 

 manure, a considerable amount of carbonate of lime, these 

 marls, you perceive, would also enrich it by the addition of 

 other ingredients useful to plants. They also usually contain 

 a minute quantity of phosphate of lime, which must contri- 

 bute to their fertilizing power. So far as their chief ingre- 

 dient, lime, is concerned, their chemical effect upon the soil 

 must be the same as that exerted by mild lime. The 

 extremely minute state of division, however, in which the 

 carbonate of lime exists in marls, will facilitate its action, 

 and the organic matter associated with it, will render its effects 

 less injurious upon soils poor in vegetable matter. Peaty 

 marls usually retain a large amount of water, which renders 

 their removal from the bogs expensive; it has, therefore, 

 been recommended to burn them ^f and Liebig, who attributes 

 their efficacy, as manure, chiefly to the changes produced 

 by the lime contained in them on the clay of the soil, 

 strongly advises that burnt marl should in all cases be 



• This marl consisted chiefly of minute shells, and had been partially 

 dried by ex}K)sure to the air ; the other specimens were peaty marls. 



t Wet marls may also be dried, by mixing thorn with shell lime, 

 which will become slaked at the expense of the water of the marl. 



