52 The Principles of Part II. 



marl to bodies which do not effervefce 

 with acids. That fuch fubftances may and 

 do fructify ground, is indubitable > but they 

 ought not therefore to be called marl. 

 Surely bodies which do, and bodies which 

 do not effervefce with acids, are very dif- 

 ferent in their nature, and ought to have 

 different names. As the name of marl, 

 then, is generally, fo let it be only applied 

 to the former clafs. The latter mould 

 have fuch names as will diftinguifh them 

 from the former. This mews what con- 

 fufion there is in the terms of agriculture, 

 and how much they ftand in need of being 

 defined. 



Exp. 22. Another quality belonging to 

 marl, by which it is diflinguilhed from 

 clay, is, that it cannot be converted to 

 brick. It is indeed very much altered by 

 a ftrong heat; it lofes its antacid quality 

 while it remains unpowdered ; and is no 

 longer difiblvable in water, as it was be- 

 fore: 



