50 The Principles of Part II. 



them. The different colours of marl make 

 no real difference as to their properties. 



Exp. 20. It is a diftinguiming and cha- 

 ra&eriftical property of this body, that, 

 when it is put into water, it falls down 

 into a powder. The clay marl dilfolves 

 much quicker than the ftone marl. This 

 quality muft be owing to the weak adhe- 

 lion of its particles j fo that the fmall force 

 with which water enters its pores, is capa- 

 ble of feparating the particles of the marl. 

 By this property it is fufficiently diftin- 

 guifhed from all the earths which we have 

 mentioned ; and particularly from clay, 

 which does not fo ipeedily admit the en- 

 trance of water. 



A s marl is fb much opened by water, fo 

 as to lofe its natural cohefion entirely, we 

 fee how much it will favour the efcape of 

 water from fuch grounds as have been ma- 

 nured with it. Clay grounds, after they 



have 



