2 ESSAYS AND OBSERVATIONS, 



lour ; fometimes it is (bfc and du6W« 

 liks clay ; fometimes it is hard and folid 

 like ftone ; and fometimes it is extended 

 into thin beds like flate. Shell marie is 

 eafily diftinguiflied by the fb^lls which 

 always appear in it. But the fimilarity 

 betwixt earth-marle and many other foffi 

 fubftances, renders it difEcult to- diftir?- 

 guifh them. 



Marles, like all the fubjeds of the 

 mineral kingdom, differ in their degrees 

 of purity. But how to difcover, with 

 certainty, the purity of any given marie, 

 is not generally known. 



From thefe circumflances, we muft 

 conclude, that raarle, tho' a fabflance 

 of ineftimable value, hath fcarce ever 

 been the fubjed of an attentive inquiry. 



In the following efliiy it is propofed, firfl, 

 to analyfe the different marie?, as newly 

 dug from the ground ; and afterwards ta 

 examine what changes they fuffer from- 

 being expofed to the air. 



SECT. 



