OF EARTH. 



37 



commend the white and gray, others the blue and red, (which I think 

 the best) according as it is more or less apt to resolve after wetting ; but 

 none of them discover their virtues for the first year : it does incompar- 

 ably on pastures ; some on arable, a good coat of compost suitable to the 

 land being first spread where you will lay it : if your marl be very unctu- 

 ous and rich, apply it less copiously ; the too thick covering is the worst 

 extreme, nor is it always to be used without allay and mixture with 

 other proper soil ; for some marls are more sandy and gritty than others, 

 and should be qualified with a contrary. Give lean and emaciated earth 

 a covering of the fattest marl ; apply hot and dry to the cold and moist : 

 and this is also to be observed in the application of all other composts 

 and medications 



calcareous. If too great a quantity of the former be used, vegetation will be greatly re- 

 tarded, it being experimentally found, that the spot on which a heap of magnesian lirae 

 has laid, will remain in a state of barrenness for a number of years ; while, on the con- 

 trary, the land on which a heap of calcareous lime has laid, will, in a short time, be pro- 

 ductive of white clover, and other natural grasses. Beds of these two kinds of limestone, 

 are often found contiguous to each other. In the neighbourhood of Doncaster, the mag- 

 nesian limestone is discovered, and at Knottingley, the calcareous kind predominates. The 

 neighbouring farmers practically know the difference, using the one liberally, and the 

 other sparingly. The difference between those two kinds of lime is this : the Doncaster 

 lime contains about three parts of calcareous earth, and two parts of magnesia. The 

 Knottingley lime is wholly calcareous. It is remarked, that magnesia is highly injurious to 

 vegetation, a circumstance that explains the reason why magnesian lime is so injurious to 

 land on which too large a quantity has been put. These two kinds of lime differ in another 

 quality. During an exposure of three months, the calcareous lime has been found to 

 absorb four-fifths of the fixed air requisite to saturate it ; while in the same space of time, 

 the magnesian lime does only absorb forty-two hundredths of that combined with it before 

 it was burnt. In the county of Derby there is found a limestone wholly calcareous, of 

 which, when burnt into lime, the farmers lay from eight to twelve chaldrons per acre on 

 their grass lands. This subject is learnedly discussed in a paper read by Mr. Tennant 

 before the Royal Society of London, and which will probably be published in their Trans- 

 actions, in the course of the present year. For this Discourse the farming world is much 

 indebted to Mr. Tennant, as it gives the ready solution of a phaenomenon that, before his 

 time, was only practically known. 



* When marl can be procured, we need not be scrupulously nice either in its kind or 

 application ; for, as far as I can learn, it never disappoints the expectations of the farmer 

 who has spirit and industry to use it. It invariably loosens a stiff soil, and gives texture to 

 a loose one : a circumstance of the utmost importance to the tillage farmer ; and indeed all 

 that is necessary for him to know concerning the nature of this earth, 



