450 NATURAL HISTORY. 



cite; going west it grows more and more bituminous, 

 until at the western extremity of Pennsylvania (Pitts- 

 burg), as also throughout the Western States, it is alto- 

 gether bituminous. Both varieties are equally excellent 

 in furnishing fuel for fires, and gas for lighting our 

 streets and houses. 



Broiun Coal Wood Coal Lignite is solid, with 

 more or less distinct traces of remains of the wood which 

 formed its origin. Burns with clear flame and an empy- 

 reurnatic odor. It occurs massive, sometimes of fibrous 

 structure ; color varying from brown to pitch black ; 

 ofttimes friable ; opaque. Fracture earthy or conchoidal, 

 luster resinous. H. = 1 to 2.5. G. = 1 to 1.4. Found 

 in the stratified or primitive mountains of the tertiary 

 period, below sandstone and clay, mostly in association 

 with pyrites. Occurs very extensively in Germany, in 

 the neighborhood of Cologne, Bonn, Eisleben, the me- 

 tallic and other mountains of Thuringia, etc. The 

 handsomest variety of lignite is Jet, which, of higher 

 luster and deeper color than the first-named, receives a 

 brilliant polish, and is set and used as jewelry. Also 

 called Gagat ; mentioned by Pliny and Dioscorides. The 

 name was derived from the river Gagas, in Syria, near 

 the mouth of which it was found ; corrupted into the 

 term jet. Found also in England. 



Turf is a mixture of plants, roots, and earths, which, 

 exposed to severe igneous action, have become combined 

 in one common structure. Color dark brown, nearly 

 black, fracture earthy; is used for fuel, but, previous to 

 burning, must be dried. A kind of coal or coke, which 

 is a better combustible than the turf itself, and burns 

 without giving forth the usual unpleasant odor, is pre- 

 pared from it. 



