THE GEOLOGIST. 
earthy matter : in the impure varieties the quantity of iron, lime, and 
aluiuina amounts, at times, to as mucli as 37 per cent. But Carb<m 
is most important as the foundation of the Coal family, divided into 
three sjjecies, — Anthracite, Common-coal, and Brown-coal or Lignite: 
these, however, are more rocks than miuenJs, and will be described 
as such. The bituminous variety of carbon, formed by its combi- 
nation with hydrogen, is classed separately as 
2. Bitumen ; Naphtha ; Petroleum; Asphaltum. Contains about 12 per 
cent, of hydrogen. Naphtha, the purest variety, is liquid ; it becomes 
thick by exposure, and is converted into Petroleum. Asphaltum is 
the solid variety. 
3. Sulphur. 
4. Water ; Ice ; Firn or Nevee. il. 
5. Corundum; Emery. Al. The granular and massive variety is Emery. 
The opaque crystalhne variety is Conuidum ; the transparent crys- 
talline blue and red varieties are respectively Sapphire and Bubi/. 
6. Quartz ; Jasper, Homstone or Cliert. Si. One of the most abundant 
minerals in nature. The pure transparent variety is Roch-crystal, and 
the blue and yellow Amethyst and Topaz. Jasper is the variety 
variously coloured by the oxides of ii-on principally. Homstone or 
Chert are names given to compact quartz substances. 
7. Opal ; Chalcedony ; Flint. Si + H. Compact or uncleavable quartz. 
Silica with 5 to 12 per cent, of water. Hyalite is the glassy trans- 
parent variety, and there are various coloured ones. The siliceous 
deposits from geysers and other hot springs are of this mineral. Opal 
differs from quartz, besides its containing water, by its much lower 
specific gravity, inferior hardness, simple refraction, and other chemical 
characters. Chalcedony and Flint are usually classed as anhydrous 
sUica, but Fuchs considers them to be a mixture of quartz and opal. 
He consequently divides compact quartz into two kinds : the one 
containing opal, like chalcedony and flint ; and the other free from 
opal, like chert. Bischof considers rock-crystal and opal as the final 
members of a series of siliceous minerals ; the former perfectly crys- 
tallized, the latter perfectly amoiijhous. 
8. Hematite, Specular-iron. Fe. The crystalline variety with metallic 
lustre is usually called specular-iron {Fer oligiste). It is an 
abundant fonu of fron, and has many sub- varieties passing into each 
other. 
9. Brown Hematite, Limnite ; Goethite; with many sub-varieties. 
+ H. Hydrous per-oxide of iron. Limnite and Goethite are 
strictly different minerals, the former containing 14, and the latter 10 
per cent, of water. 
10. Magnetite, Magnetic Iron. A combination of 1 atom of per-oxide 
