[ xvii ] 



Since it has not been ufual to confider the 

 earths and flones as the fame, in reg;ard to the 

 principles of which they coniift, and only diffe- 

 rent from one another by the greater or leffer 

 -hardnefs and coherency of their particles; I hope 

 for excuie, in not being able to proiecute this 

 Eilay fo far as to point out a particular e :rth 

 for each kind of (tone. Perhaps alfo iome of 

 the mineral bodies are already lo much harden- 

 ed, that no earths of this Rind are to be found ; 

 or, perhaps, the little knowledge w r e have of 

 them is owing to the negledt or not collecting 

 earths with the fame earneftnefs as w T e do flones 

 and ores. If, therefore, all the earths which 

 are ranged in certain modern fyflerns, and 

 there diltinguilhed from one another, in regard 

 to the difference of their colours and places 

 where they are found, had fallen into the hands 

 of Mr. Port, and been tried by him in the fire, 

 as he has tried the (tones, and been defcribed in 

 his Lkhogeognefia, it is very probable that we 

 now fhould know thefe bodies better, and their 

 number would certainly be lefs perplexing. 



The hints which are here given may, how- 

 ever, tend to promote the intended point for 

 the future \ and then perhaps the earths will be 

 found not to be quite of fo many different kin;is 

 as I have here h-en obliged to divide them into, 

 for want of perfectly knowing their affinities and 

 their feveral origins; becaufe we have (Iron?' rea- 

 ions to believe that the calcareous and am laceous 

 earths are the two principal ones, of which all 



b the 



