PHYSICAL AND i^fTERARY 3? 



Thus it appears, that marles diiFer 

 from other calcarious fubftanees, only by 

 containing a certain proportion of clay. 

 On which account, the clafs of calcarious 

 bodies will admit of a divifion into fuch 

 fubftanees as in the air fall down into^ 

 powder, and fuch as do not. 



SECT. 



Iftal contact, t'he apptication of water to that matte 

 Vrould produce no effe<5t. On the other hand, when 

 marie of confiderable purity is calcined, if the calcarioua 

 particles were in contact with one another, not even the in-* 

 creafed cohefion of the clay would be able to prevent theic 

 reparation, confidering the quantity of calcarious eartt» 

 contained in fuch marles, and the force with which that: 

 earth, after calcination, explodes in water. But, if your 

 conceive the calcarious particles as feparately involved 

 in clay, which in its natural ftate readily falls down ia 

 *rater, and after burning, denies admittance to that 

 fluid, all fhephsenomena are eafily accounted for. Befides 

 all this, fads are not wanting to juftify the fuppofuioiv 

 cf this arrangement. Acids, however ftrong, cannot 

 extraft any calcarious earth from calcined marie, excepc 

 fuch particles as lie upon the broken furface ; and whea 

 thefe particles are thus carried away, the furrounding 

 |)art;c!es of clay, tho' more eafily feparated, ftill retaia 

 their former fituation and attachments ; which (hows 

 *liat futh particles are fixed to one another, and caa 



ftipporC 



