ORGANIC FORMS. 337 



any fossil remains lias often been supposed to indicate a 

 period previous to any organic formations. The inor- 

 ganic constituents of matter are probably of prior origin 

 to the organic combinations ; the vessel was constructed, 

 upon which the organic creation was to float in space 

 before any vital organisms were created. The supposed 

 evidences in favour of the assumption that there was no 

 organic life during the formation of the oldest rocks we 

 know, are in some respects doubtful ; and we can well 

 understand that changes may have been induced in the 

 earlier rock formations, by heat or by other powers, quite 

 sufficient to destroy all traces of organized forms. It 

 was long thought that phosphoric acid was not to be 

 detected in rocks which are regarded as of igneous origin; 

 and since this acid is peculiarly a constituent of organic 

 bodies, this has been adduced as a proof that the plutonic 

 rocks must have existed previously to the appearance of 

 vegetable or animal life upon the surface of the globe. The 

 researches of modern chemists have, however, shown that 

 phosphoric acid is to be found in formations of granitic 

 origin, in porphyry, basalt, and hornblende rocks.* If, 

 therefore, we are to regard this substance as of organic 

 orgin, the rational inference is against the speculation ; 

 but there is no more necessity for supposing phosphorus 

 to be formed in the animal economy than in the mineral 

 kingdom, from which it will probably be found the 

 animal obtained it. 



Without attempting to enter into any account of the 

 apparent progress of life over the earth, it appears 

 desirable that some description should be given of the 

 kinds of plants and animals which we know to have 

 existed at different epochs. We shall thus learn, at least, 

 some of the prevailing characteristics of the earth during 



* Fownes, On the Existence of Phosphoric Acid in Rocks of 

 Igneous Origin ; Phil. Trans. 1844, p. 53. Nesbitt, Quarterly 

 Joitrnal of the Chemical Society. 



