THE GEOLOGICAL TIME- SCALE. 191 



is distinguished from the Secondary and all older beds by con- 

 taining some representatives of the faunas now living. 



In this earliest attempt to estimate time-relations by biologi- 

 cal data, Lyell, as others of his time;, considered species to be 

 sharply defined natural groups, and therefore it was that the rela- 

 tions between a fossil fauna and its recent representatives could 

 be expressed in mathematical terms, indicatirrg the number of 

 identical species. The principle underlying the classification, 

 however, was of a deeper nature, and concerned the orderly suc- 

 cession of faunas and floras in time. From the application of 

 this method of time -analysis to the Tertiary beds, it was 

 extended to an analysis of the whole series of geological forma- 

 tions on the basis of their organic remains, and the Lyellian 

 classification took the place of the older Lehmann classification 

 as follows : 



In place of Tertiary we have Cainozoic. 

 " " Secondary " Mesozoic. 



" " Transition " Palaeozoic. 



" " Primitive " Azoic. 



This latter classification and nomenclature was gradually 

 built up, and mainly by English Geologists, as the Lehmann 

 and Wernerian classification was largely elaborated by German 

 and French Geologists. 



Edward Forbes proposed to divide the known faunas and 

 floras into two great groups. Neozoic (modern) and Palaeozoic 

 (ancient). The two terms Palaeozoic and Protozoic were proposed 

 about the same time. Palaeozoic by Sedgwick, for the formations 

 known to be fossil iferous, extending from his lower Cambrian 

 upwards to include Murchison's Silurian system, and Protozoic 

 was a provisional name proposed for pre-Cambrian rocks which 

 might be found to contain fossils. (Sedgwick, Proc. Geol. Soc, 

 Vol. II, p. 675, London, 1838). 



In his Silurian System, Murchison proposed Protozoic in the 

 following words : " For this purpose I venture to suggest the 

 term " Protozoic Rocks," thereby to imply the first or lowest 



