Neocomian. 

 Aptian. 



M. AlciJe il'Orbigny on Livintj and Fossil Molluscs. 65 



Jurassic Formation. 



Infenor Lias, belonging to the zone of 

 Grypkcea arcuata, and below it. 



Middle Liax, belonging to the zone of 



First stage, the Lias ( Gryphcea cyrnblum, up to Gryphcea 



arcuata. 



Superior Lias, above Gryphcea cym- 

 biuin. 



c, J T> ^1 • ^ I Lower Oolite. 



Second, iJathonian stage --, . /^ j-^ 



' ^ I Great Oolite. 



I Inferior Oxford stage (Kelloivay rock). 



Third, Oxford stage } Middle Oxford stage (Oxford-clay). 



{ Superior Oxford stage (Coral-rag). 



T^ ., T' ■ • 1 • ^ I Inferior, or Kimmeridgian. 



rourth, Kimmeridgian stage... < „ •' • n .i v 



' o s I Superior, or i'ortlandian. 



Cretaceous Formation. 

 First stage, Neocomian 



Second stage, Albian or gault. 



™, . , . ™ . f Turonian, or chloriteous chalk. 



1 bird stage, luroman { „ . ,.^ , „ 



° I Senonian, or white chalk. 



Tertiary Formation. 



r Inferior, to the coarse limestone. 



First stage, Parisian J Superior, or coarse limestone and su- 



I, perior beds. 



Second stage, Sub-Appenine. 



m.- J i. TA-i • I In this latter period we find none but 



1 faird stage, Diluvian . , . . 



° [ species now living. 



After these general considerations, we may add a few 

 words on the more special facts, the study of which is of di- 

 rect interest to palaeontologists ; and we shall begin with the 

 simple accidents of fossilisation in shells. 



" The state of preservation in shells may often deceive the 

 observer, and lead him to separate different states of the 

 same shell as distinct species. Shells, whether they have 

 been buried by the strata of the earth in the place where they 

 occur, or have been conveyed by currents, are generally ar- 

 ranged in zones in the fossiliferous formations. According to 

 their geological age, or the longer or shorter period they 

 have remained in these sti'ata, they are completely or par- 



VOL. XLVII. NO. X<'III. — .JULY 1849. E 



