208 Oil Lime and Marls^ 



careous matter contained in gypsum (which is said to 

 be Z'^ per cent) were separated, it might make a very- 

 good manure, at the rate of three hundred bushels, more 

 or less, to an acre. All the English writers on this 

 subject consider the different varieties of lime and 

 gypsum valuable in proportion to the quantity of cal- 

 careous matter which they respectively contain ; and 

 that this class of manures has most effect upon soils 

 which contain the least calcareous matter, previous to 

 their application ; upon this principle, how will they 

 account for the effects produced by one or two bush- 

 els of gypsum to an acre, not only upon lands which 

 never have been limed, but also upon limed land, a 

 fact confirmed beyond a doubt, by the universal ex* 

 perience of our farmers ? It is true, indeed, that marl 

 is less valuable, in proportion to the quantity of extra* 

 neous substances which is mixed with it ; but in this 

 case, the calcareous matter has not entered into a che- 

 mical combination with the extraneous particles ; but, 

 though mixed, are still distinct ; and these generally 

 consist of clay, sand, or peat-moss, which are in their 

 nature more inert than the calcareous matter. 



Dr. Anderson gives the best account of the natural 

 history of shell marl, that I have any where met with ; 

 but it appears to me, that he has never had the oppor- 

 tunity of using it ; because his account of its effects 

 upon the soil will only apply to \vhat he calls clay marl; 

 which is nothing more nor less than mixing different 

 soils. But the use of what is called clay marls and stone 

 marls, are nov/ almost universally laid aside ; the ex- 

 pense of hauling.bcing found, in most cases, to exceed 



