26 Elements of Mineralogy. 



colour as the foregoing, the pureft forts alone 

 are placed here. 



Calcareous Incrujlations* 



Thefe are generally found on branches or 

 roots of trees, and fometimes on ftones of 

 different kinds, the moft remarkable of thefe 

 incruftations is that found on the roots of 

 pines, called Qfteocolla^ which Mr. Margraaf 

 found to confift chiefly of calcareous Earth, 

 mixed with a fmall proportion of filiceous, 

 and volatile alkali, together with fome vege- 

 table parts* 



Calcareous Petrifactions. 



Thefe confift of calcareous ftones, in the 

 form of animal or vegetable fubftances, the 

 former are called Zoophytes^ the latter Phy-> 

 tholites. 



The moft remarkable of the former are, ift, 

 Thofeof the Cbr^/clafs, of a ramified and tubu- 

 lar form as coral, madrepores, millepores, 

 aftroites, 2d, Thofe of the clafs of fea worms, 

 belemnites, which are of a conic or cylyndrical 

 form. Afleritz and Entroctfo which have a 

 ftarry appearance. 3d, Thofe of the tefta- 

 ceous clafs, as nautllitcs^ ammonites ^ echini y 



Agaric 



