Related Geological Conditions 49 



remains of fishes, eurypterids, and molluscs of freshwater 

 habitat in such ironstones are a noteworthy feature. 



VII. Petroleum and its probable relation to fishes. 



Another highly important geological phenomenon, that 

 we hope to show is intimately connected with the life, death 

 and fossilization of fishes, can now be taken up. Through- 

 out many parts of the world, and at times on gigantic scale, 

 reservoirs of natural oil, of petroleum, of gas and of 

 asphalt have been discovered, and today constitute highly 

 important commercial products. 



From the upper Silurian rocks, upward to comparatively 

 recent Tertiary formations, rich deposits of these have been 

 tapped and extensively utilized. But the question of the 

 possible source and mode of formation of such bituminous 

 deposits, has called forth a wide variety of views. These 

 views have been synopsized by Engler and Hofer (2^:11, 

 passim), also by Redwood (25; I, 268-283). An inorganic 

 and an organic source haVe alike been claimed. The former 

 we will not further discuss, since we regard the extremely 

 varied products of petroleum as without an approach or 

 parallel, in any synthetic action effected through expenditure 

 of inorganic energies, but as being exactly such as might 

 be called "end-products" of destructive analysis amongst 

 plants and animals. But some advocates of the "organic" 

 theory of origin have suggested that petroleum and its 

 products represent decomposed plant substances, produced 

 either from accumulation of resin and allied hydro-carbons 

 formed by trees, or from decomposition — possibly under 

 heat and pressure — of vegetable fats and fixed oils de- 

 veloped in the tissues. 



Now at the present day the tissues of many Hepaticae 

 or scale-mosses and of the true mosses, also the spores of 

 club mosses are rich in fixed oils. But though we would not 

 deny origin of a very limited amount thus, the total pos- 

 sible accumulations of these or of resinous hydrocarbons, 

 seem wholly insufficient to explain the huge — almost inex- 

 haustible — supplies of petroleum throughout the world. 



If we turn now to the animal world, most groups of 

 animals contain supplies of a fatty nature. But to explain 



