326* PHYSIOGRAPHY. CLASS u. 



massive varieties ; Rose Quartz, confined to translucent rose- 

 red and milk-white massive varieties ; and Prase, which is 

 only of a dark leek-green colour ; Common Quarts at last com- 

 prehends all those varieties not included in any of the preced- 

 ing subspecies. There are several massive varieties of com- 

 mon quartz, which consist of granular particles of composition. 

 If these diminish so much in size as to become impalpable, 

 also their transparency and lustre is somewhat diminished, 

 and several kinds of conchoidal and splintery fracture ap- 

 pear, if specimens of these varieties be broken. This gives 

 rise to new species, according to the old acceptance of the 

 word. Hornstone is always compound, translucent on the 

 edges, and either of a splintery dull fracture, or glistening 

 and glimmering and conchoidal. Thus splintery Hornstone 

 and conchoidal Hornstone are formed, and either of them 

 may produce Woodstone, if it appears in the shape of petri- 

 fied wood. The varieties of common Flinty slate are most 

 like Hornstone, but shew on a large scale an imperfect 

 slaty fracture and various dirty grey colours ; those of Ly- 

 dian stone, which forms the second kind of Flinty slate, pos- 

 sess an even, glimmering fracture, and a greyish-black colour. 

 Flint is a compound mineral like the two preceding ones, but 

 translucent at least on the edges, and possesses a perfect, flat 

 conchoidal, glimmering fracture. Float-stone, a variety of 

 rhombohedral Quartz, which has likewise been considered 

 as a particular species, consists of a delicate tissue of mi- 

 nute crystals, visible under a powerful magnifier, and de- 

 monstrates hornstone and flint, into which it insensibly 

 passes by having its grain closer, and of which it often con- 

 tains nodules, to be varieties of the same natural-historical 

 species. Common Quartz is sometimes found in reniform 

 and stalactitic shapes, consisting of granular particles of 

 composition, sufficiently large to be observed and separated 

 from each other. If the thickness of these individuals be so 

 much diminished that at last they become impalpable, the 

 different varieties of Calccdony are formed, occurring in the 

 above mentioned external shapes. The difference in the 



