50 Evolution and Distribution of Fishes 



requisite conditions from an animal source one must almost 

 of necessity postulate: (a) the existence throughout the 

 entire geological record from the Silurian upward of a most 

 prolific type of organism; (b) the production in such of 

 a substance or substances that would directly, or by decom- 

 position-change, give rise to petroleum and its products; 



(c) the comparatively sudden destruction on an extensive 

 scale of great masses of the organism, and the accumu- 

 lation of these masses in special pockets or layers of strata; 



(d) the comparatively rapid decay of the accumulated or- 

 ganic masses in freshwater or possibly in salt water, and the 

 setting free of the more stable oil from the rapidly de- 

 composing albumen products; (e) the gradual absorption 

 of this oil into some stratum of highly pervious nature; 

 (f ) the nearby presence of lower and upper impervious beds 

 that would bottle up and conserve the oil; (g) the sub- 

 sequent anticlinal — more rarely synclinal — uptilting of 

 the entire rock mass, and its exposure to frictional, volcanic 

 or other source of heat; (h) the' resulting splitting up of 

 the accumulated oils, under pressure and fairly high tem- 

 perature into petroleum products. 



While we would not deny that in some cases and only 

 to a very small extent other groups of animals than fishes 

 have contributed, and probably did contribute, to this out- 

 come, the writer would strongly afl'irm — from all the evi- 

 dence to hand — that fishes formed the source of supply to 

 a preponderating extent. Further, all of the above require- 

 ments are fulfilled when we follow out the geological 

 records of fishes. Thus many palaeontologists have often 

 commented on the oily aspect of the matrix in which fish 

 remains occurred from the time of the Devonian onward. 

 And this applied, not to one or a few species, but to 

 many, distributed over the successive periods. 



Murchison early drew attention to the possible origin 

 of bituminous rocks in the following words (26:542): 

 "The Flagstones of Caithness, which were first described 

 by me In the year 1827 under the name of 'Bituminous 

 Schists' (Trans. Geol.Soc.s 2, v. 2 (1827)213) are in many 

 places Impregnated with bitumen, chiefly resulting from the 

 vast quantity of fishes embedded in them. Their most dur- 



