;<2 DOMAIN I. SIDEROUS. 



It would indeed be a singularity that, while 

 basaltin occurs so often in a columnar form, a 

 substance composed of the same ingredients should 

 never assume that appearance. Yet perhaps the 

 columnar form of basaltin may itself be partly 

 owing to the impalpable fineness of the ingredients 

 allowing an exact scission, or crystallisation, which 

 coarser materials would not admit; as crystals 

 are generally composed of finer ingredients than 

 amorphous substances. 



* 



MODE III. BASALTIN. 



Characters. Texture finely and almost impalpably granu- 

 lar, sometimes vesicular ; on a large scale strati- 

 fied, rising like successive steps, whence the 

 Swedish name trap. It sometimes presents dis- 

 tinct concretions, of a finer or of a coarser grain. 

 It seems to split in rhomboids, while the colum- 

 nar sometimes lapses into globular forms *. 



Hardness basaltic, or between marble and fel- 

 spar, about 800 of the scale of Quist. Fracture 

 sometimes even, sometimes conchoidal. Frag- 

 ments amorphous > not very sharp. 



Weight siderose. 



* Mr. Watt, Ph. Tr. 1804, observes, that raelted basalt passes 

 into globules, before it assumes the compact texture. 



