PHYSIOGRAPHY. 107 



Calcareous Spar. 



resents the greater part of the pure varieties of the species. The sim- 

 ple varieties, and such compound ones in which the indviduals 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, Oolite or Roestone was in- 

 cluded ; the roundish grains, however, of the latter, consist of columnar 

 individuals, disposed like the radii of a sphere, and frequently showing 

 distinct traces of cleavage. Common fibrous- Limestone is produced by 

 columnar composition in massive varieties; the fibrous Calcs inter by 

 the same, but appearing in various imitative shapes. Pea-stone or Pi- 

 solite consists of diverging columnar individuals, collected into cuived 

 lamellar ones, forming globular masses, which are again agglutinated by 

 a calcareous cement. Each of the globules generally contains a grain, 

 of sand, which is of Quartz or Feldspar. Compact limestone passes into 

 Chalk, if the individuals are more loosely connected with each other, so 

 that the whole assumes an earthy appearance ; and Hock milk or Agaric 

 mineral is formed, if the mass contains so many interstices, that it seems 

 to possess but a sinall degree of specific gravity. Calcareous tufa, a 

 recent deposit formed on the suiface of the earth, is often cleavable, and 

 thus possesses all the properties of the variety called Calcareous Spar. 

 Slate spar or Argentine, is produced by a lamellar composition in mass- 

 ive varieties, in the direction of the face ol composition Fig. 119 of twin- 

 crystals, contained in thin parallel layers. Swinestone, Anthracoliite, 

 Marl and Bituminous Limestone* are impure and mixed varieties, part- 

 ly of calcareous spar, partly of compact limestone. 



The pure vaiieties of Calcareous Spar are entirely soluble, with effer- 

 vescence in nitric or muriatic acid. In the common fire they are infu- 

 sible, but part with carbonic acid, and become converted into quick-lirne. 

 2. Analysis. 



According to the analyses of several of the first chemists, Calcareous 

 Spar consists of Lime - - 56-0 . . . 57-0 



Carbonic acid - - 43 ... 44 



The varieties very often contain a small portion of oxide of iron, silica, 

 magnesia, alumina, carbon or bitumen. 



3. Calcareous Spar rarely enters into the composition of rocks. In 

 most ca.ses, the more considerable masses of it form particular beds in 

 other rocks, or constitute rocks themselves: the latter consist chiefly of 



