110 On Plaister of Paris. 



vous effects will be visible, as acids of all sorts are 

 mimical to vegetation. 



In this way we account for the different effects produc- 

 ed by gypsum, and also for the gypsum, brought from 

 certain places, being more valuable than that brought 

 from others. In many cases its value will depend upon its 

 containing more calcareous earth than acid. Upon lands j 

 therefore, where no stimulating substance has been ap- 

 plied, and which contain little or no calcareous earth 

 in themselves, this sort of gypsum will be a good ma- 

 nure ; accordingly, in America, where the soil in most 

 places is composed almost entirely of vegetable earth, 

 arising from the decayed herbage, and the deciduous 

 parts of the trees which have grown and decayed there 

 since the creation, and where scarcely a particle ofcalca^ 

 reons earth is to be met with^ this sort of gypsum will 

 stimulate the soil, and produce good effects; even in this 

 country, upon virgin soils, which contain no principles 

 of that sort, its effects will be similar ; hut upon lands 

 ivhich have been long in a state ofcidtivation, which have 

 been frequently manured with substances containing much 

 alkaline matter^ or which have received a due proportion 

 of calcareous earthy its effects will not be perceptible, 

 unless an enormous quantity be used. But in cases 

 where the acid prevails, its bad effects will be visible at 

 once. In all cases, therefore, where gypsum is intended 

 to be used,zY ought to be a mutter of serious inquiry^ 

 firsts whether the land has been previously limed ? and 

 next, whether the acid or calcareous earth prevails in 

 its composition ? If the land possesses in itself no cal- 

 careous matter, the gypsum, which contains most of it^ 



