LIMITATION OF SPECIES IN TIME. 155 



theory assumes : they prove a continued similarity of or- 

 ganized beings during successive geological periods, not- 

 withstanding the extensive changes in the prevailing 

 physical conditions which the country they inhabited may 

 have undergone at different periods. In whatever direc- 

 tion tin's theory of the origin of animals and plants, under 

 the influence of physical agents, is approached, it can no- 

 where stand a critical examination. Only the deliberate 

 intervention of an Intellect, acting continuously, accord- 

 ing to one plan, can account for phenomena of this kind. 



SECTION XXIII. 



LIMITATION OF SPECIES TO PARTICULAR GEOLOGICAL PERIODS. 



Without entering into a discussion respecting the 

 precise limits within which the fact is true, there can no 

 longer be any doubt that not only species, but all other 

 groups of animals and plants, as well as individuals, 1 

 have a definite range of duration. The limits of this 

 duration, as far as species are concerned, generally coin- 

 cide with great changes in the physical conditions of the 

 earth's surface ; 2 though, strange to say, most of those 

 investigators who would ascribe the origin of organized 

 beings to the influence of such causes, maintain also that 

 species may extend from one period to another, which 

 implies that they are not affected by such changes. 3 



When considering, in general, the limitation of species 



1 Compare Sect. XIX. BRONN, (H. G.,) Index palaeontologi- 



2 ELIE DE BEAUMONT, Recherches cus ; Stuttgardt, 1848-49, 3 vols. 8vo. 

 sur quelques unes des Revolutions de ORBIGNY, (A. D',) Prodome de Pa- 

 la surface du Globe ; Paris, 1830, 1 laeontologie stratigraphique univer- 

 vol. Svo. selle, etc. ; Paris, 1850, 2 vols. 12mo. 



3 For indications respecting the MORRIS, (J.,) Catalogue of the 

 occurrence of all species of fossil or- British Fossils ; London, 1854, 1 vol. 

 ganized beings now known, consult 8vo. ; 2d edit., 1854, 1 vol. Svo. 



