V] RAISING OF THE FERTILITY LIMIT 81 



only. The tufa-like variety is good for crops. The 

 white kind found in streams is extremely rich ; it is 

 hard to the touch ; if too much is put on it burns the 

 soil. The red kind is called acaumimarga, it contains 

 hard lumps of petrified sandy fragments. This is 

 broken on the ^eld itself and in the first years the 

 stubble is only cut with difficulty on account of the 

 stones. It is put on very sparsely, only half as much 

 being used as of the other kinds. They think it is 

 mixed with salt. Either of these kinds put on the 

 land will last for 50 years. 



"Of the fatty marls the chief are the white 

 varieties. There are several of these: the sharpest 

 is the one above mentioned. Another is the silvery 

 chalk. It is sought for deep in the ground, wells 

 being frequently sunk 100 ft. deep with the mouth 

 narrow and the shaft widening out as in mines. This 

 is the kind most used in Britain. It lasts for 80 years 

 and there is no instance of anyone who has put it on 

 twice in his life time. A third white marl is called 

 glisomarga, it is a fullers chalk mixed with rich soil 

 more productive for herbage than for crops, so that 

 after the harvest and before the next sowing there 

 springs up a rank growth to be cut. When it is 

 applied to crops it produces no other vegetation. It 

 lasts for 30 years ; if put on too thickly it strangles 

 the soil. The columbina marl is called eglecopala by 

 the Gauls, it is equally fertile. It is turned up in 



B. 6 



