682 



PETROLEUM. 



interior valleys." The bitumen of California 

 is Miocene, while that of Mexico, the West 

 India Islands, and Peru, is Eocene. 



It will be seen that there is an area, esti- 

 mated at 200,000 square miles in the Missis- 

 sippi valley, the formations of which are no- 

 where later than the Coal-Measures, which 

 yields petroleum at many points and often in 

 vast quantities. Another area yielding bitu- 

 men, of vast extent, reaching from California 

 to Bolivia is everywhere Tertiary; while on 

 the Eastern Continent a belt of correspond- 

 ing age, so far as is known, extends from the 

 North Sea to Java. At present, the greatest 

 volume of petroleum issues from rocks older 

 than the Carboniferous, while the greater num- 

 ber of localities producing bitumen are Eocene. 

 In Canada and West Virginia it rises from 

 sandstone strata beneath the crowns of anti- 

 clinals, as also in northwestern Ohio, where 

 the rock is the Trenton limestone. In Penn- 

 sylvania the so-called "oil-sands" appear to 

 lie in the inclosing rocks in long narrow belts 

 or sheets, far beneath superficial erosion, like 

 sand-bars in a flowing stream. They run 

 through a vast accumulation of sediments, 

 from the lower Devonian to the Upper Car- 

 boniferous, and lie conformably with the in- 

 closing rocks dipping gently to the southwest. 

 The Bradford field at a depth of about 1,800 

 feet, 100 square miles in extent, by from 20 

 to 80 feet in thickness lies with its lowest 

 southwestern edge submerged in salt water, 

 and its northeastern edge filled with gas, orig- 

 inally under an enormous pressure. In Gali- 

 cia the sandstones that hold the oil are impli- 

 cated in the folds of the Carpathians and much 

 distorted ; while at Baku the sands appear to 

 be lenticular masses inclosed in a stiff blue clay. 



Chemistry. The first analyses of petroleum 

 were ultimate, and showed that it consists of 

 carbon and hydrogen, with occasional small 

 quantities of sulphur and nitrogen appearing as 

 impurities. There are, however, several varie- 

 ties of petroleum, to some extent dependent 

 upon the age of the rocks from which they 

 issue. All, or nearly all, Trenton limestone 

 petroleum contains sulphur and more or less 

 nitrogen. The Upper Devonian and Subcar- 

 boniferous petroleum of Pennsylvania is a very 

 pure hydrocarbon, and, along with the Eocene 

 petroleum of Galicia, contains paraffine. The 

 Miocene petroleum of California appears to be 

 a mixture of unstable fluids, compounds of car- 

 bon and hydrogen, containing a notable amount 

 of nitrogen. These, with the Mexican and South 

 American oils, do not contain paraffine, and 

 readily oxidize into asphaltum. There are 

 many other petroleums of this class, and others 

 still have been little examined chemically. The 

 proximate examinations that have been made 

 show that petroleums from different localities 

 are quite unlike. The petroleum of Pennsyl- 

 vania, eastern Ohio, and West Virginia, con- 

 tains a large number of the paraffine series in 

 varying proportion, in mixture with a smaller 



and indefinite proportion of the olefine series. 

 Other petroleums of nearly identical composi- 

 tion contain small quantities of the benzole 

 series with an increasingly large proportion of 

 unstable compounds that oxidize into asphal- 

 tum. Those of Galicia are of this description. 

 Those of California have been little examined, 

 but appear to be almost entirely confined to un- 

 stable, easily oxidized oils. The Russian oils 

 from Baku consist of the additive compounds 

 of the benzole series, which have the same per- 

 centage composition as the defines, and contain 

 less hydrogen than the paraffines. Burmese 

 petroleum contains a notable proportion of the 

 benzole series. All of the compounds derived 

 from petroleum absorb oxygen when exposed 

 to light, and become colored and viscid. The 

 residues from the distillation of petroleum 

 have remarkable fluorescence. It is not sup- 

 posed that these substances are present in the 

 natural oil, although it is not impossible that 

 they are. 



Origin. The theory that petroleum is the 

 product of chemical reactions still in progress 

 in the earth's crust was originally put forward 

 by Bertholet, and has since been continued on 

 the same line by Mendeljeff, the eminent Rus- 

 sian chemist. Their theories are based on the 

 results of laboratory experiment?, and assume 

 the existence in the earth's crust of powerful 

 deoxidizing agents, such as the alkali metals, 

 cast-iron, spiegeleisen, etc., which in contact 

 with steam and carbonic acid set free the hy- 

 drogen and carbon, causing them to unite in 

 the nascent state and produce mixtures of hy- 

 drocarbons resembling petroleum. These the- 

 ories require conditions nowhere proved to 

 exist in nature. 



Petroleum is, without a reasonable doubt, pri- 

 marily derived from a partial decomposition of 

 animal or vegetable remains. In the Trenton 

 limestone and other Silurian rocks it has proba- 

 bly been produced by the transformation of low 

 forms of animal life. The petroleum issuingf rom 

 the Miocene shales of southern California is also 

 of animal origin. The first of these oils is often 

 found hermetically sealed in the cavities of 

 large fossils and in geodes in limestones rich in 

 animal remains. These older oils are rich in 

 sulphur, and those of California are compara- 

 tively rich in nitrogen also. They are dark, fetid, 

 and in many instances, particularly those of 

 California, they rapidly change on exposure to 

 the air to a black, viscid mass, which finally 

 becomes solid asphaltum. The California oils 

 undergo changes due to a sort of putrefactive 

 process, as pools of oil have there been ob- 

 served to become infested with maggots, like 

 a pool of blood when similarly exposed. These 

 fetid animal oils are difficult to refine, and are 

 chiefly used as fuel. 



The Devonian oils of eastern Ohio, Penn- 

 sylvania, New York, and West Virginia are 

 with equal certainty derived by spontaneous 

 distillation from the deposits of shales that un- 

 derlie the oil-sands, and, where exposed along 



