440 NATURAL HISTORY. 



structures like marble, in which case it forms large beds 

 of rock and even mountains. When met with as a crys- 

 tal, it is mostly colorless ; luster vitreous ; sometimes, 

 however, found gray, green, yellowish, very rarely red 

 or blue, but in every case translucent. As a compact 

 stone its hue is light groy or grayish-blue, and. with the 

 exception of white marble, always impure. Fracture 

 conchoidul ; effervesces with acids. II. = 3.0. G. = 2.5 

 to 2.73. Lime is among the most useful of the miner- 

 als ; calcareous spar is employed as a solvent in Metal- 

 lurgy. Marble is of infinite importance in sculpture, 

 for which purpose that brought from the quarries of Car- 

 rara and the island of Paros is best ; that used for 

 building material is called granular limestone. The 

 more compact limestone, of variegated veins and shadings 

 and on account of its receiving a beautiful polish, is also 

 called marble, and applied to all purposes and varieties 

 of stone manufactures, as slabs for tables, pedestals, cor- 

 nices, etc. This species Avhich often exhibits variegated 

 shadings of color, and breaks out into thick slabs, is of 

 varied structures and markings. Sienna Marble is yel- 

 low with cloudings ; Bird's Eye is compact limestone, 

 with crystal points disseminated through it ;* Ruin Marble 

 is yellowish, with brownish shadings or lines, represent- 

 ing castles, towers, and cities in ruins ; other marbles 

 are also named after the fanciful figures they represent ; 

 the markings are due to infiltrated oxyd of iron or man- 

 ganese. Ruin Marble is among the Florentine varieties 

 of Calc. Lithographic stone is a compact grayish or 

 yellowish-gray limestone of very even texture and cou- 

 choidal fracture ; used in lithography. That of Solen- 

 hofen near Munich is most noted. The use of Chalk, a 

 member also of this family is well known. Calcareous 



