60 
HAROLD’S DISCUSSIONS. 
and some in Asia, near the Caspian Sea, as many as 
25,000 barrels a day. 
The United States, in 1900, produced 63,362,704 
barrels, valued at $75,752,691. This oil is known as 
petroleum—two Latin words which mean rock-oil. 
Petroleum was known even to people of ancient times. 
It has been discovered in all civilized parts of the 
world, not only in Paleozoic rocks, but in later for- 
Fig. 34.—Oil-field in southern California. 
mations as well. In Pennsylvania petroleum is found 
in sandstone strata of the Upper Devonian formation ; 
in Ohio in porous limestone of the Cambrian ; in Cali¬ 
fornia and in Europe in the Tertiary. Like water, 
it collects in porous rocks and seams, usually limestone 
or sandstone between two layers of shale. Oenerally 
gas is found in the upper part of the fissure, oil next, 
and water in the bottom. Salt beds are frequently 
found in connection with oil. 
