PETROLEUM, ASPHALT, AND BITUMEN. 383 



leum are found in the different countries of the globe, often asso- 

 ciated with salt, gypsum, sulphate of iron, and mineral springs. 

 A considerable number of these deposits are asphaltic or petro- 

 leum-bearing basins, of greater or less richness, the working of 

 which requires the boring of wells, or the excavation of galleries 

 permitting a tolerably exact determination of the manner of oc- 

 currence of the substances. Nowhere do the works furnish any 

 evidence of the existence of reservoirs or cavities comparable to 

 the caverns of mountainous regions ; but everywhere the hydro- 

 carbons are in the state of impregnation or mixture with the 

 rocks in which the workings are made. When they exist in a 

 viscous or solid condition, there is reason for presuming that this 

 state or manner of being is due to particular phenomena of con- 

 centration operating at the moment of deposition or after it. The 

 existence of veins or of eruptive beds, ancient or recent, is no- 

 where established in a certain and indisputable way, but it may 

 be that fissures existing in the rocks have been filled, either from 

 above or laterally, by a posterior displacement. 



In attempting to account for the origin of the hydrocarbons, a 

 distinction may be made between two states in which they pre- 

 sent themselves, whether on the surface or in the depths of the 

 soil. The initial state, or that of formation, is represented in the 

 stratified beds, where a series of superposed layers is presented. 

 The substance exists, impregnating the rock, and, more rarely, in 

 viscous or solid bituminous masses. The second state, that of 

 alteration or transformation, is met in the beds which have been 

 modified by dislocations, posterior to the solidification of the mat- 

 ters which were deposited in a movable or plastic state. To these 

 dislocations may be attributed the natural petroleum wells which 

 have been known from antiquity, as well as the flows of vis- 

 cous bitumen which in some regions become solid on exposure to 

 the air. 



The slow distillation of marine bodies may be likened, to a cer- 

 tain extent, to the processes of conservation of fossil wood in the 

 bottoms of marshes, peat bogs, etc., under the mud. But while 

 the absence of air is suflicient to assure the preservation of these, 

 the presence of an entirely impermeable envelope is necessary to 

 prevent complete decomposition into volatile gases such as takes 

 place with all animals simply buried under water. 



The presence or existence of natural springs of petroleum in 

 the vicinity of mountainous regions is explained, not by disloca- 

 tions of the ground, but by the fact that the formation of the re- 

 liefs is anterior to that of the mineral oil. Instead of regarding 

 these springs as available as guides in researches, they should be 

 regarded as signs of the approaching exhaustion of the arenaceous 

 strata impregnated with oil ; these reservoirs not being suscep- 



