1S4 MENACANE, AND ITS ORES. 



this fossil has only occurred in rocks belonging to primitive 

 trap, or in sienite, the last crystallization which took place 

 within the primitive period, and must therefore be considered 

 as a later production than rutile. Here a consideration of 

 the laws of crystallization countenances the observations on 

 the order in which the primitive rocks follow one another. 

 The rutile, consisting of few and simple elements of cotem- 

 porary origin, with a granite, in which rock crystal occupies 

 the place of quartz, and adularia that of common felspar, 

 sufficiently bespeaks a period, when the solution being purer 

 and more tranquil, furnished an earlier and purer crop of 

 crystals; while the confused and irregular crystallization of 

 primitive trap and sienite, together with the greater impurity 

 of the felspar, and very compounded nature of the horn- 

 blende and rutilite, indicate an inferior purity of the solu- 

 tion, and, consequently, later precipitation of the crystallized 

 mass. 



Species III. 

 Nigrine. 



THIRD SPECIES. 



NIGRINE. 

 Nigrin of Werner. 



External cha- 

 racters. 



Observations 

 on nigrine. 



EXTERNAL CHARACTERS. 



The colour is dark brownish black, passing into velvet 

 black. Is found in larger and smaller angular grains, and 

 pebbles. Externally, moderately glistening. Internally, 

 principal fracture is glistening; the transverse fracture mo- 

 derately glistening. Lustre, adamantine. The principal 

 fracture is imperfectly foliated, with a single cleavage; the 

 transverse fracture is flat, and imperfectly conchoidal. The 

 fragments are indeterminately angular, and sharp-edged. 

 Perfectly opaque. Semihard. Brittle. Gives a yellowish 

 brown streak. Heavy, in a moderate degree (4,500^. 



OBSERVATIONS. 



This fossil is r«adily distinguished from menacane, by its 

 stronger lustre and superior hardness, the colour of the 

 streak, and by its not being in the least fliagnetic j which 



also 



