30 ESSAYS AND OBSERVATIONS 



cohefion diminiflied by the influence of 

 moifture. But, when thefe fubftances 

 are calcined and thrown into water, as 

 the calcarious particles then recede front 

 mutual contatft with a force which the 

 cohefion of the particles of fand, if there 

 is any, is not fufficient to refili, the whole 

 compofition muft immediately fall into 

 powder *, 



Thu§ 



. * It would appear, that in clay-marles, the particles 

 •f clay are difpofed in fuch a manner, as to touch one 

 another, and, at the fame time, to prevent the mutual 

 contadl of the calcarious particles. According to this 

 difpofition, each particle of calcarious earth will be fur- 

 rounded with a coat of clay. It is difficult to conceive 

 how, without fomej fuch arrangement, the changes 

 mentioned above fliould be produced. Unlefs the clay 

 cetnents the calcarious earth, water, which only influ^ 

 ences the clay, would fcarcely bring about the refolu- 

 tion of marie ; nor would the calcination of this fub- 

 llance, which tranfports the property of relenting in 

 ■water from the clay to the calcarious earth, produce th« 

 effeSs afcribed to it above. Befides this, water, fo far 

 as is yet known, only deHroys the attraftioa of the par- 

 ticles of clay to one another, not the attradion of thofe 

 particles to any other fubftance ; therefore, unlefs th^ 

 particles of clay contained in aqy marl? were in mu- 

 tual 



