326 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



debris is cast upon the banks at the mouth of the river, is covered with 

 mud and penetrated with saline matter, while a large part is carried far 

 away by the current, and furnishes valuable building material to the 

 inhabitants of the glacial zone. 



The bitumens, the petroleums, and the naphthas are hydrocarburets, 

 more or less condensed, which proceed from the decomposition of large 

 deposits of vegetable matter, imprisoned between the sedimentary strata, 

 and submitted to variable pressure. Such is the conclusion Ave have 

 attained, thanks to the researches of synthetic chemistry, which teaches 

 us that the products of the distillation of wood can, under certain con- 

 ditions of temperature and of pressure, be transformed into more com- 

 plicated carburets. 



Petroleum is largely diffused in the terrestrial crust. In Europe, and 

 especially in Gallicia, several pits have recently been discovered. Asia 

 is quite rich in this product, but in North America it has become the 

 object of a very important and extended industry. The tubes bored for 

 the purpose of obtaining this oil pass ordinarily through the ferruginous 

 clay, the sandstone, the conglomerate, and the bituminous schists 

 before reaching the bed of oil confined between two strata of refractory 

 slate, containing the fossil remains of Stigmaria and other plants of the 

 Coal period. When the drill reaches the bed of oil, a regular explosion 

 of gas takes place, the latter consisting in most cases of a mixture of 

 carbonic acid and hydrocarburets. This explosion is followed by a con- 

 tinuous jet of oil, which shoots up sometimes to a height of more than 

 30 yards. Both gas and oil being eminently inflammable, many disas- 

 ters occur in boring the petroleum-wells. The yield from these pits 

 is sometimes as much as 4,000 gallons of oil in twenty-four hours. The 

 daily product of all the wells of the United States may be estimated at 

 50,000 gallons. The oil is generally of a deep-brown color, and only in 

 a few cases is clear and transparent. A simple distillation suffices to 

 render it fit for ordinary use.* 



We may consider as an organic product the gas disengaged in several 

 l)arts of Italy and in Transylvania, and now burning at Bakou, on the 

 Caspian Sea. The Ho-tsing or wells of fire in Central Asia, of which 

 Humboldt has left a very detailed description, are equally gaseous ema- 

 nations, proceeding from the subterranean decomiiositiou of vegetable 

 substances. 



Peat is a recent deposit of vegetable matter, the formation of 

 which appears to have some analogy with that of oil. The remains of 

 all kinds of plants may contribute to the increase of peat-bogs, but in 

 order that marshes become peat-bogs certain conditions are necessary 

 favoring the development of the plants of which the largest part of them 

 are formed. Thus the water must not be comijletely stagnant, must not 

 be impregnated with slime nor be liable to any great rise or fall, must 

 not be very deep and not rapid in motion, while the bed of the marsh 



*A. Gesuer, Quart. Journ. Geolog. Soc, London, t. xviii, p. 3. 



