1897.] PETROLEUM IN TPIE CAVITIES OF FOSSILS. 125 



form in the cavities of fossils or in other open spaces. Moisture in 

 such quantity as is absorbed by many dense rocks would tend slowly 

 to remove liquid hydrocarbons, just as it might drive them from 

 the cells of vegetable tissue. The region of least resistance to the 

 movement of the oil would be a cavity. The accumulation of oil 

 in open spaces in fossils would thus result from its displacement 

 from adjacent, or perhaps distant, parts of the rock by water, 

 which would tend to produce a retreat of the oil. If thus impelled 

 by the movement of moisture through the rock the oil would grad- 

 ually assume the liquid form if it passed into a cavity. The cells of 

 corals and other open spaces might thus become reservoirs capable 

 of holding collectively considerable quantities of oil. 



It is true that before the original sediment became hardened into 

 rock, the proportion of water present must have been considerable. 

 In accordance with a commonly accepted view the process of petro- 

 leum formation was not completed until long after the sediments 

 with their enclosed organic matters had been consolidated. The 

 oil would then have been expelled from the rock, little by little, as 

 it was being gradually produced. In this case also the movement 

 of the oil might have led to its being caught in liquid form in cav- 

 ities, or if it oozed out at the surface of the rock stratum it might 

 have been absorbed by a more porous rock, or caused by pressure 

 of water to flow off through sand-rocks of more open texture. 

 The movement of the oil through the rock, displaced from the 

 interstices in which it had originally collected, would have been 

 accelerated as the transition from solid organic tissues to liquid 

 oil had become advanced. 



Water, if present in a rock of fine texture, could not by the 

 action of capillarity alone be drawn upward so as to collect in 

 liquid form in a cavity. The same statement is true of petroleum. 

 But the presence of moisture in the interstices of a rock in which 

 petroleum is being generated or in which it is stored in minute 

 pores or spaces might lead to a gradual accumulation of oil from 

 the bulk of the rock into relatively larger spaces such as the cavities 

 of fossils. 



Jaccard {Le Fetrole, 1895, P- ^34) ^^^^ described the occurrence 

 of bitumen in the cavities of fossil moUusks in the Val de Travers 

 in the Jura mountains. Such cases might be regarded as represent- 

 ing a later stage in a series of changes, the original liquid petroleum 

 having passed into solid bitumen long after it was accumulated in 



