86 THE PROSPECTOR'S HANDBOOK. 



Petroleum. 



A fluid, darker in colour than naphtha, sometimes black. 

 Naphtha and petroleum contain 84 to 88 per cent, of car- 

 bon, the rest hydrogen. Asphalt, in addition to carbon 

 and hydrogen, contains oxygen and a little nitrogen. In 

 California it is found in strata belonging to the Tertiary 

 age. In Colorado and other Western States, to the Cre- 

 taceous. In North Carolina, to the Triassic. In West 

 Virginia, to the Coal measures. In Kentucky, it occurs near 

 the base of Carboniferous Limestone. The West Pennsyl- 

 vania oil strata belong to the Devonian age. The anticlinal 

 ridges are said to be more favourable than the synclinal 

 ones (see page 15). 



GYPSUM (alabaster). 



Crystallization derived from a right rhomboidal prism. 

 Colour white, grey, black, &c. 



When pure, is clear and translucent, and of pearly lustre. 

 In hardness most varieties can be scratched by the nail. 

 S.G. 2 -3. In composition is a sulphate of lime. Before B.F. 

 becomes white and opaque, and is easily crumbled. All 

 varieties, when heated and reduced to powder and mixed 

 with water harden while drying. Gypsum (from which 

 plaster of Paris is manufactured) occurs in recent Tertiary 

 formations, and also in the various other formations as old 

 as the Silurian. Is often associated with beds of rock salt 

 as in Cheshire. Does not effervesce in acids : hence distinc- 

 tion between it and limestones and other carbonates. 



APATITE. 



A mineral very rich in phosphate of lime, and, after 

 treatment, used for dressing the soil. 



Cleavage not well marked. 



Colour white, grey, greenish, &c. 



Streak white. 



Is transparent to opaque. 



H. 4-5 to 5 ; S.G. 2'9 to 3-3. 



Some varieties are phosphorescent when heated. Before 



