PHYSICAL AND LITERARY. 45 



Th u s it is manifeft, that calcarious earth 

 and clay conftitute a fubftance pofTefTed 

 of the properties of marie ; and that a 

 mixture of the fame earth and fand, even 

 in equal proportions, is not deftitute of 

 the mod diflinguiiliing chara(5lersof lime- 

 ftone, Thefe circumftances ferve to fup- 

 port the account formerly given of the 

 natural compofition of marie and lime- 

 done, whilft at the fame time they fhow, 

 that marles, conlidered as calcarious bo- 

 dies, may furpafs many lime-ftones in 

 purity. Maries, however, are limited 

 in the proportion of their calcarious earth. 

 They cannot, according to my obferva- 

 tions, contain much above four-fifths 

 of it. Lime-ftone may confifh entirely, of 

 this earth. 



From the affinity betwixt marles and 

 lime-ftone, we may fee whence it happens, 

 that a bed of the latter is often found 

 interpofed betwixt two beds of the former. 

 The calcarious earth in both is the fame. 

 The fubfidence of clay in the one cafe, 

 and fand or nothing in the other, along 

 with that earth, makes all the difference. 



Among 



