■ (298) 



confidet it as well defervlng attention. Black 

 ilioerl in the mafs conftitutes the greateft 

 part of it. It is found in pieces furrounded 

 by a grey earthy crufl:, which attaches to 

 the tongue, and is a decompofition of the 

 fhoerl. The cruft in fome pieces is ex- 

 tremely thin, but in others extends to a 

 greater or lefs depth ; and in fome leaves 

 only a black flioerlaceous point in the mid- 

 dle. Thefe fmall pieces are ufually angu- 

 lar ; w^hence we may infer that they have 

 not been in a fluid ftate. They are all 

 bound together by a cement, fmall In quan- 

 tity, of a pale yellov/ colour, and a vitreous 

 afped:, which is likewife changed by the de- 

 compofition. The breccia in the furnace is 

 reduced to a black and frothy fcoria. 



The decompofition of this breccia appears 

 to be a confequence of the action of the at- 

 mofphere and of tim„e. The fhoerlaceous 

 fragments evidently Ihew that they exifted 

 previouily to the vitreous fubftance ; which 

 paffing over them when it was in a fluid 

 :(late, included them within it, and formed 



one 



