42 WHAT EVOLUTION IS 



by Woodward (1665-1728), Valis- 

 nieri (1661-1730), Smith (1769- 

 1829), and especially by Cuvier 

 (1769H1832). Cuvier further rec- 

 ognized that the older rocks con- 

 tained fossils of a simpler type than 

 the more recent ones did, and he ex- 

 plained this difference by assuming 

 that periods of cataclysmic destruc- 

 tion alternated with periods of special 

 creation. This doctrine was carried 

 to an extreme by d'Orbigny (1802- 

 1857) who claimed for the past some 

 twenty-seven such alternations. But 

 the idea of cataclysmic alternations 

 was defeated by the school of uni- 

 formitarians, whose advocates, like 

 Lyell ( 1 797-1 875), saw in the present 

 forces of nature an explanation of 

 the past and supported the idea of 

 continuity, not interruption, in the 

 organic series. By these steps the 

 modern conception of fossils and 



