FUNDAMENTAL RELATIONS OF ANIMALS 101 



ods, between which great physical changes have undoubtedly taken 

 place. Thus the facts indicate precisely the reverse of what the theory 

 assumes: they prove a continued similarity of organized beings dur- 

 ing successive geological periods, notwithstanding the extensive 

 changes in the prevailing physical conditions which the country they 

 inhabited may have undergone at different periods. In whatever di- 

 rection this theory of the origin of animals and plants under the in- 

 fluence of physical agents is approached, it can nowhere stand a 

 critical examination. Only the deliberate intervention of an Intellect, 

 acting consecutively according to one plan can account for phenom- 

 ena of this kind. 



SECTION XXIII 

 LIMITATION OF SPECIES TO PARTICULAR GEOLOGICAL PERIODS 



Without entering into a discussion respecting the precise limits 

 within which this fact is true, there can no longer be any doubt that 

 not only species but all other groups of animals and plants have a 

 definite range of duration, as well as individuals. ^^^ The limits of 

 this duration, as far as species are concerned, generally coincide with 

 great changes in the physical conditions of the earth's surface; ^^^ 

 though, strange to say, most of those investigators who would ascribe 

 the origin of organized beings to the influence of such causes main- 

 tain also that species may extend from one period to another, which 

 implies that these are not affected by such changes. ^^^ 



When considering in general the limitation of species to particular 

 geological periods, we might very properly disregard the question 

 of the simultaneity of the successive appearance and disappearance 

 of Faunas as in no way affecting the result of the investigation, as 

 long as it is universally conceded that there is no species known 

 among the fossils which extends through an indefinite series of geo- 



^ Compare Sect. xix. 



"^ £lie de Beaumont, Recherches sur quelquesunes des revolutions de la surface du 

 globe (Paris, 1830). 



la'! Por indications respecting the occurrence of all species of fossil organized beings 

 now known, consult Heinrich G. Bronn, Index palceontologicus (3 vols., Stuttgart, 

 1848-1849); Alcide d'Orbigny, Prodrome de Paleontologie stratigraphiqiie iiniverselle 

 (2 vols., Paris, 1850); John Morris, Catalogue of the British Fossils (London, 1854). 



