I believe, did he find less than three per cent, of carbonate 

 of Lime, and one contained as much as 11 and l-4th per 

 cent. In a soil of eight inches in deptb, three per cent. 

 I calculate, would amount to about 32 tons per acre, which 

 at the rate of exhaustion by the crop alone, as computed 

 by Professor Johnston, but without taking into account 

 any other sources of waste, would last about 130 rotations, 

 or about 500 years. But as much of the straw and turnips 

 are again returned to the land in the shape of manure, 

 which contains part of the Lime previously extracted, such 

 land might probably not be exhausted of that ingredient 

 (at least by the crops) for three times that period. Much 

 land, not situated near the Limestone districts, I believe 

 contains as little as only 1-1 0th per cent., or only about 

 22 cwt. per acre ; and that is the description of soil which 

 most frequently wants replenishing ; as, if you compute the 

 exhaustion from all causes to amount to ^ cwt. per acre 

 per annum, (which in the common course of cropping I 

 believe to be pretty near the mark,) all the stock of Lime 

 will be extracted in about fifteen years, provided that none 

 is returned in any shape. Professor Johnston in his lectures 

 mentions, that Lampadius tried an experiment in order to 

 test the amount of exhaustion of Lime, stating that he 

 mingled Lime with the soil of a piece of ground till it 

 was in the proportion of 1.19 per cent, of the whole, 

 and he determined subsequently, by analysis, the quantity 

 of Lime contained in each of the three succeeding years. t 



Carbonate of Lime. 



The 1st Year it contained L19 per cent. 



2nd do. 0.89 



3rd do. 0.52^ 



4th do. 0.24 



But what are the sources of exhaustion beyond what is 

 extracted by the crops ? The chief, no doubt, is from the 



I 



