Earths. 



ther process unnecessary to detail, is the real 

 base or constituent of all clays, formerly called 

 argillaceous earth; for all the clays which are 

 found native are more or less combined with 

 other extraneous matters. 



CLAYS are among those earths which most 

 abound in nature. There are immense strata of 

 them, and they make a part of every rich soil. 

 The idea which naturalists and others have of 

 them is that of natural substances, the purest of 

 which are firm, and have a sort of unctuosity, 

 and which, by rubbing with the finger, receive a 

 polish. They imbibe moisture, so that when 

 applied to the tongue it adheres to them. From 

 their attraction for water, they are always found 

 moist in their natural state ; if more water is 

 added, they form a soft and ductile paste, which, 

 when thoroughly burnt and dried, becomes hard, 

 stony, and impenetrable to water. 



As clay, when wrought together, becomes 

 impenetrable to water, it is made use of to retain 

 water in ponds, &c. This is the reason that 

 when cattle are allowed to tread a clayey soil in 

 wet weather, the plants die that grow there ; for 

 the clay being mixed with the water by their feet, 

 the ground will be too tough for the plants to 

 spring up in, especially when the clay, thus trod 

 together, is afterwards dried by the heat of the 

 sun, for then it will prevent the rain from pene- 

 trating to the roots of the plants. 



Clays differ much in consistency : some melt 



