88 PHYSIOGRAPHY. CLASS 11. 



nular, the individuals being of various sizes, and 

 even impalpable ; faces of composition irregularly 

 streaked, uneven, and rough. The individuals co- 

 here more or less firmly. If the composition be 

 impalpable, fracture becomes splintery, uneven, flat 

 conchoidal, or even ; on a large scale it is some- 

 times slaty. The fracture is earthy in those va- 

 rieties in which the individuals cohere but slightly. 

 3. Composition lamellar ; the individuals more or 

 less thin, and often bent ; face of composition some- 

 times rough, and possessing a pearly lustre. Glo- 

 bules formed in cavities ; plates, of various kinds of 

 composition. 



OBSERVATIONS. 



1. The species of rhombohedral Lime-haloide is not yet 

 determined with perfect purity and correctness by all mi- 

 neralogists. Even in the system of Abbe H AU Y, it includes, 

 though only as an appendix, substances which do not belong 

 to the species. Pearl-spar, Dolomite, Rhomb-spar, have 

 long ago been separated from the species of rhombohedral 

 Lime-haloide ; and this separation is fully confirmed by the 

 examination of the angles, the degrees of hardness and of 

 specific gravity, which has produced the assumption of the 

 three following species. It cannot yet be maintained, that 

 the number of those species of the present genus, whose forms 

 belong to the rhombohedral system, is thus exhausted ; on 

 the contrary, it is highly probable, that there exist several 

 others, the determination of which has hitherto been im- 

 possible, on account of the want of an exact natural-histo- 

 rical examination. The same takes place in other genera. 

 Differences in the admeasurement of forms, in hardness, 

 specific gravity, &c. f if they be constant and not connected 

 by transitions, necessarily produce different species. Yet 



