324 FUCOIDES IN THE COAL FORMATIONS. 



horizons is very limited, the value of what is known already and applied to the identifi- 

 cation of strata is demonstrated and strengthened by every new discovery. 



$8. DOES PETROLEUM ORIGINATE FROM THE DECOMPOSITION OF MARINE PLANTS? 



Considering the question of the origin of our deposits of petroleum, some geologists 

 have expressed the opinion that they might be due to the decomposition of marine plants, 

 as coal is the result of the decomposition of a terrestrial vegetation. This conclusion 

 is but natural, for there exists an evident correlation between the formation of both kinds 

 of deposits of bitumen. But this relation cannot be, or at least has not yet been, estab- 

 lished by direct proofs or experiments, and that is probably the cause why the subject has 

 not been studied more in detail. 



$9. FECUNDITY OF THE MARINE VEGETATION AT THE PALEOZOIC AGES. 



There is no doubt that the marine vegetation of the Palaeozoic ages can be compared, 

 for luxuriance, and in some measure for its composition also, to the terrestrial vegetation 

 of the coal epoch. From the Upper Devonian down to the Lower Silurian, some strata of 

 shales are not only covered, but indeed filled, sometimes for hundreds of feet in thickness, 

 with fossilized forms of Hydrophytes. These evidences of a primordial vegetable world 

 are far more numerous than the remains of land plants in the shales of the Coal Measures. 

 Nevertheless, they appear to belong to plants of a soft tissue, mere cellular, probably 

 mostly uncellular vegetables, the debris of which had not by much the same chances of 

 fossilization. 



The superabundance of vegetation testified by fossil remains in Palaeozoic ages is in 

 accordance with one of nature's most evident laws. The amount of carbonic acid gas is 

 acknowledged to have been, at the Palaeozoic times, far greater in the atmosphere, and 

 also in the water of the seas, than it is now. The prodigious luxuriance of the vegetation 

 of the coal period is rightly ascribed to this fact. It cannot be supposed that in the sea 

 the vegetation, which is there also the intermediate agent between animal life and unor- 

 ganized bodies, gaseous or mineral, should have been in a diminutive state when its action 

 was the most in demand, like its development, for the purification of the water and the 

 transformation of the superfluous carbonic acid gas into organism and oxygen. 



We have no proofs from fossil remains that the Hydrophytes of old attained a very 

 large size. The largest circular fronds of Fucoides Cauda-galli show a diameter of about 

 one foot ; the greatest length of the branching Fucoides in the Chemung is from two to 

 three feet. But we cannot judge all the vegetable representatives of an epoch from a 

 few fossilized specimens. These may have belonged to a species of a more compact organ- 

 ization, or to some kind of Corallines, which had their surface covered with a hard crust 

 of lime, while other groups of a soft, mere cellular tissue, which had representatives of 

 large size, have been totally decomposed and destroyed. There is no need however of this 

 hypothesis, on the size of the Palaeozoic Algae, to argue by comparison on the fecundity of 



