Sect. III. Agriculture and Vegetation. 63 



fait, unlefs the foil were frequently turned 

 over; and even then much of the fait 

 would be defended by the oleaginous par- 

 ticles of the foil. Marl appears to me to 

 be the proper cure j for that abforbent earth, 

 having a ftronger affinity to the acid of 

 vitriol, than what the iron has, will unite 

 itfelf with the acid, feparate the chalybeate 

 particles, render them infoluble in water, 

 and confequently unfit to enter the vefiels 

 of plants. A conliderble mare of the 

 good effects of marl in all grounds, may, 

 perhaps, be owing to this fpecial effect, 

 viz. the deftruction of a body, which, 

 in proportion to its quantity, deftroys all 

 vegetation. 



THERE is another foffil body very fimi- 

 lar to marl in its appearance, and fome 

 of its qualities, and may be miftaken for 

 it. It is called by fome writers foap- 

 rock, from its fimilitude to foap, and its 

 being often found in rocks -, though I have 

 known it lying on the furface in great 



quan- 



