12ri PETROLEUM IN THE CAVITIES OF FOSSILS. [Feb. 5, 



would be left to impregnate the calcareous skeleton. If, on the 

 other hand, the process was continued until the organic matters 

 were buried under deep sediments and exposure to oxidation had 

 ceased, then more distinct 'signs of a deposit of sediment over the 

 entire reef should be looked for. 



The conditions for effective oxidation of organic matters are 

 rendered more complete under water by the presence of bacteria, 

 and these must have aided greatly in promoting the final change of 

 the tissues of the dead coral animals into nitrates, ammonia, car- 

 bon dioxide and water. In stream beds and under sediments the 

 products of the decay of animal matters are mainly gaseous, and 

 the contents of the coral cells must have been almost wholly lost in 

 volatile form before a process of change into petroleum could have 

 been begun in the much diminished residue of the original organ- 

 isms. 



It is possible that the occurrence of petroleum in the cells of a 

 modern coral reef may find an explanation in a phenomenon often 

 observed in the case of natural gas. I have elsewhere (^Journal of 

 the American Chemical Society, 1895, p. 801) called attention to 

 the fact that on stirring the gravel which lies at the bottom of many 

 streams in western Pennsylvania, it is common to find that gas bub- 

 bles are disengaged, and that such an accumulation of gas may 

 occur where the stream flows over sandstone, covered by gravel a 

 few inches only in depth, and where the character of the gravel 

 renders it unlikely that gas could have originated locally. In such 

 cases it is probable that the occurrence of gaseous hydrocarbons is 

 due to an escape to the surface from deep-lying rock strata. 



Petroleum escaping from the interstices of a rock might accumu- 

 late in the cavities and cells of dead corals. A slow oozing of 

 petroleum from the surface of the ground is a well-known phenom- 

 enon in various parts of the oil regions. 



The occurrence of petroleum in cavities of fossils might be 

 traced to a former condition of wide distribution of oil throughout 

 the rock, that is, in a form in which it is known to be present in 

 limestones and shales in many places. The gradual access of moist- 

 ure to the pores of a rock so impregnated would tend to cause a 

 slow displacement of the oil. Water, insufficient to appear in 

 liquid form upon a surface of fracture, might still suffice, as it grad- 

 ually saturated the rock under the influence of capillary attraction, 

 or of pressure, to displace the oil and cause it to accumulate in liquid 



