268 CAUSES OF FERTILITY AND STERILITY [chap. 



bulk. The "thin" limes partake somewhat of the 

 nature of a cement, setting after mixture with water, 

 and are more esteemed by builders than the "fat" 

 limes, which harden with extreme slowness and are 

 chiefly employed for plastering and kindred work. 

 Naturally the " fat " limes are preferable from an agri- 

 cultural point of view, both for their purity and the 

 finer condition into which they fall; unfortunately few 

 of the lime works grind the white lime in the ordinary 

 course of trade, as they do the builders' lime. 



The lime made by burning the Magnesian Lime- 

 stone which occurs in Durham, Yorkshire, Derby- 

 shire, and Notts, is disliked by farmers and regarded 

 as injurious rather than beneficial to the land. It 

 contains 50 to 80 per cent, of lime and 4 to 40 per 

 cent, of magnesia, which latter constituent may be 

 the cause of the ill effects. 



The following analyses show the mean composition 

 of several samples of "fat" and "poor" lime, being 

 "white" and "grey" lime respectively, made from the 

 Upper and Lower Chalk of the North Downs : — 



In place of lime, chalk may often be used with 

 advantage when it is readily accessible ; for example, on 



