4 PETRIFACTIONS AND THEIR TEACHINGS. 



course of this investigation. As, however, the arrangement 

 adopted in the Gallery is botanical and zoological, not geolo- 

 gical, the uninitiated visitor will have no difficulty in under- 

 standing the general descriptions of the most important 

 specimens submitted to his notice. 



To remind the observer of the relative age and position of 

 the deposits, and the meaning of certain geological terms which 

 we shall sometimes have occasion to employ in the following 

 narrative, a brief table of the British strata 1 is subjoined. 



A TABLE OF THE FOSSILIFEROUS DEPOSITS OF GREAT 

 BRITAIN. 



MODERN OR HUMAN EPOCH. 

 ALLUVIAL and VOLCANIC deposits. 



POST PLIOCENE OR DILUVIUM.2 

 DRIFT; BOULDER-CLAY, &c. 



TERTIARY EPOCHS. 



PLIOCENE ; the upper and newest Tertiary. (Norwich Crag.) 

 MIOCENE; or middle Tertiary. (Suffolk Crag.) 



EOCENE : the lowermost or most ancient Tertiary. (London, Hants, and Isle of 

 Wight. Paris basin.) 



SECONDARY EPOCHS. 



IU r Ch Ik 'th fl'nt (S ut h an( * nor ^i Downs of Sussex, 

 Chalk marl and firestone; or Upper Green Sand. (Godstone, 

 Undercliff of Isle of Wight.) 

 Gait or blue chalk marl. (Folkstone.) 

 (Shanklin Sands, (Kentish-Rag. Kent. Isle of 

 Green sandJ Wight.) 

 (.Atherfield or Neocomian beds. (Isle of Wight.) 



(Weald clay, and Sussex and") Wealds of Sussex and Kent, and 

 WEALDEN ) Petworth marbles. V the South coast of the Isle of 



FORMATION. j Hastings sands and clays. ) Wight. 

 VPurbeck strata. (Isle of Purbeck.) 



1 Strata are sedimentary deposits that have been formed in the beds 

 of lakes, rivers, and seas, and have subsequently been displaced and 

 elevated above the water by physical causes. A series, or group of 

 strata, is termed a, formation ; and the fossil remains found in one series 

 or formation differ more or less completely from those of another. 



2 Called also the Quaternary or Diluvian period : these deposits can- 

 not be definitively separated from those of the Modern or Human epoch. 

 The gravel beds near Geneva, which closely resemble the newest tertiary 

 drift in materials and position, abound in bones of animals, almost all 

 of which belong to existing species. See M. Pictet's " Palceontologie." 



