A TREATISE ON THE CONNECTION OF 



SOILS, 

 ARGILLACEOUS OR CLAYEY. 



THERE is no clayey soil that is pure and free from 

 sand; and there are but few clays that are free from a 

 mixture of calcareous matter, magnesia, vegetable and 

 animal matters, mineral oil, tind other mineral or metal- 



lic substances : some clays are of a much more unctuous, 

 and, as it were, greasy nature, than others. They do not 

 differ more in this respect, than they do in the appear- 



ance they assume when submitted to a moderate degree 

 of heat. Those clays which are the most unctuous and 

 greasy to the touch, are by calcination changed to a black 



^colour. This must be owing either to their containing 

 animal or .vegetable matter, although previous to calci- 

 nation it escapes observation; or the inflammable matter 

 in the clay may exist in the state of .a colourless mineral 



toil, adhering obstinately to the clay, and not capable of 

 being separated from it by water, with which oil can 

 hold no union; yet capable of being changed into a black 

 carbonaceous matter by the action of fire. A due mix- 

 of day serves the important purposes of retaining 



in 



