Argillaceous Genus. 75 



more fufible. This fpecies of marl falls to 

 pieces more difficultly, either in water or air, 

 than calcareous marl. 



Indurated marls, of a quadrangular form, 

 have been called Ludi helmontii. 



Fuller's Earth. 



This is moftly of a white, grey, bluifh, or 

 yellowifh colour, compact, femi-indurated, 

 of a lamellar texture, and often conchoidal in 

 its fracture ; confifting of very fine particles, 

 fmooth and fomewhat foapy to the touch : it 

 burfts and is diffufible in water, with which 

 it often froths like foap : it does not effervefce 

 with acids ; in a ftrong heat it melts into a 

 flag. Microcofmic fait affects it but (light- 

 ly ; mineral alkali more powerfully, and with 

 much effervefcence, but bora:$ melts it moft 

 completely. 



Different fpecimens of it, from various 

 countries, afforded Mr. Bergman from 47 

 to 60 of filiceous Earth, from 1 1 to 25 of ar- 

 gillaceous, from I to 6 parts of magnefia, 

 from 3 to 7 of mild calcareous Earth, from 

 3 to 5>5 f dephlogifticated iron, and from 

 15 to 1 8 of water, mixed with a very minute 

 proportion of marine acid ; but this laft was 

 found only in a few of them, Its fulling 



power 



