MODE V. SMECTITE. 77 



surface. They lie on chalk, covered with sea 

 sand, which still retains its brackish flavour. 

 Above that is fullers' earth, nearly eleven feet in 

 depth, and then chalk, and different kinds of 

 clay ; then a common sort of sand : and so on 

 to the surface, which is gravel. 



It does not effervesce with acids, nor is it dif- 

 fusible in water, in which it does not froth like 

 soap, as some have asserted. It is used in what 

 is called the fulling of broad cloth, an operation 

 which consists in extracting the grease. 



Abroad, it has been found in Saxony, Alsace, 

 and Sweden, always forming beds of more or 

 less thickness. In England it commonly ap- 

 pears between beds of sand-stone. 



The earth brought from Cimolus, which is 

 described by Pliny as used in medicine and in 

 bleaching, has again been discovered, by Mr. 

 Hawkins. It is mingled with small particles of 

 quartz; but this circumstance does not prove it 

 to be a decomposed granite, as an accidental 

 mixture of silex occurs in many substances. 



Fullers' earth, from Reading, in Berkshire. 



The same, with incumbent sea sand and 

 oyster- shells. 



The same, from Ryegate, in Surry. 



The same, of a coarser kind and darker co- 

 lour, with imbedded crystals of yellow barytes. 



