OttDEIl I. KHOMBOHEDRAL LIME-HALOIDE. 89 



they require most accurate examination ; and this, on the 

 other hand, must serve as a proof that the measures of the 

 angles within a correctly determined natural-historical 

 species, are in fact invariable. 



The distinction of several species within that of rhombo- 

 hedral Lime-haloide, and the division of them into seve- 

 ral sub-species and kinds, as it used to be in the older Mi- 

 neralogy, depends chiefly upon the mode of composition, 

 and upon admixtures and impurities, with which the indi- 

 viduals have been affected in their formation. Of these, 

 Limestone, if we except Flosferri (p. 83.), represents the 

 greater part of the pure varieties of the species. The 

 simple varieties, and such compound ones in which the in- 

 dividuals are of considerable size, and easily cleavable, have 

 been called Calcareous spar, compound varieties of granular 

 still discernible individuals, are granular Limestone, both 

 comprehended under the head of foliated Limestone. If the 

 granular composition disappear, compact Limestone is formed, 

 under which denomination also the Oolite or Roestone was 

 exhibited. The roundish grains, however, of the latter, 

 consist of columnar individuals, disposed like the radii of a 

 sphere, and frequently shewing distinct traces of cleavage. 

 Common fibrous Limestone is produced by columnar compo- 

 sition in massive varieties, the fibrous Calcslnter by the 

 same, but appearing in various imitative shapes. The lat- 

 ter must be carefully distinguished from similar formations 

 of prismatic Lime-haloide. Pea-stone or Pisolite consists of 

 diverging columnar individuals, collected into curved la- 

 mellar ones, forming globular masses, which are again ag- 

 glutinated by a calcareous cement. Each of the globules 

 generally contains a fragment, sometimes of considerable 

 size, of some heterogeneous matter, as quartz, granite, &c: 

 Compact limestone .passes into Chalk, if the individuals are 

 more loosely connected with each other, so that the whole 

 assumes an earthy appearance ; and Rock-milk or Agaric 

 mineral is formed, if the mass contains so many interstices, 

 that it seems to possess but a small degree of specific gra- 



