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CHAPTER IV 

 GEOLOGICAL PALAEONTOLOGY 



(A) STRATIGRAPHICAL 



(I) ZONES AND HEMERAE 



:HROUGHOUT the last hundred years, Geologists 

 have found in fossils efficient and reliable evidence 

 for the chronological classification of sedimentary 

 rocks. The claim made by William Smith, that " Strata 

 [can be] identified by organized fossils," has been substan- 

 tiated in the main ; and the principle has been applied to 

 refinements undreamed of by that pioneer. Subdivision 

 of the geological record into the great eras Palaeozoic, 

 Mesozoic and Cainozoic is based on palaeontological 

 evidence, as the names imply ; relatively brief periods 

 of time, such as hemerae, are recognized solely by 

 detailed study of fossils. 



The classification of rock-systems was a fairly simple 

 problem for early stratigraphers, who, starting from 

 preconceived ideas, believed in the catastrophic doctrine 

 that the faunas of successive periods were distinct, in 

 members and origin. Long years of palaeontological 

 research were necessary to prove that the " dating " 

 evidence afforded by fossils is not so sharply defined, 

 while growth of realization of the process of evolution 

 was fostered by, and contributed to, the knowledge that 

 each faunal assemblage is intimately connected with 

 its antecedents and successors. When species ceased 



