CHAPTER XI. 



HANTONIAN PERIOD. 



HAYING- elsewhere stated my conviction that the 

 Lyellian divisions of Tertiary time cannot be re- 

 garded as systems or groups of equivalent geological value 

 to those which are recognized as divisions of Secondary 

 time, 1 1 need only here explain that no more than two such 

 Tertiary systems can be admitted ; for the first of them, in- 

 cluding the Eocene and Oligocene series, the name Han- 

 Ionian has been proposed, and for the second, which in- 

 cludes the Miocene, Pliocene, and Pleistocene series, the 

 name Icenian has been suggested. The same nomencla- 

 ture will be used in the present volume ; and it may be ob- 

 served that the importance of the break between the Oli- 

 gocene and the Miocene has recently been recognized by 

 M. de Lapparent. 2 



The simplest division of the British Eocene series into 

 groups of fairly equivalent value is as follows 3 : 



jy ( Hordwell Sands and Barton Clay. 



\ Bracklesham and Bournemouth Beds. 

 j f j Lower Bagshot Sands and London Clay. 



( Reading Beds and Thanet Sands. 



1 Geol. Mag.," 1885, p. 293, and " Historical Geology," 1886, p. 36. 



2 "Manual of Geology," 1886, second edition, pp. 1120, 1164. 



3 This chapter was written before Professor Prestwich read his paper 

 " On the Correlation of the Eocene Strata " (" Geol. Soc. Proc./' Dec. 

 21, 1887), in which he proposes the same division of the Eocene series. 



