446 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JunC 7, 



remark by Agassiz in his ' Poissons Fossiles.' At the same time, 

 notwithstanding the presence of so many old forms, the London 

 Clay shows, in another portion of its fish-remains, a close analogy with 

 the ordinary families and genera existing at the present day — some 

 in warmer climates, but a not inconsiderable number identical with 

 those frequenting the existing coasts*. 



The Corals of the London Clay and of the Bracklesham Sands 

 belong chiefly to different families ; the latter are closely related to the 

 forms prevalent in the Paris Basin ; whilst the former, with a certain 

 amount of resemblance to some of these species, exhibit marked dif- 

 ferences and divergent relations. Of the Turbinolidce there are 

 four genera in the London Clay, three of which belong to that 

 section, the " Cyathince," which has several representatives in the 

 Chalk and Gault especially. Of the section Turbinolmce there are, 

 on the contrary, one species in the London Clay and seven in the 

 Bracklesham Sands. The Hupsammidce furnish also four genera ; 

 the species which occurs in the London Clay, the " Stephanophyllia 

 discoides," is of the flat lenticular form peculiar to the Cretaceous 

 section of this genus. The other three genera occur in the Brackle- 

 sham Sands. The PennatulidcB and Gorgonidce, of which there are 

 three species in the London Clay and one in the Bracklesham Sands, 

 are however distinctly Tertiary families. 



The Mollusca present a more decided ttrtmry fades, but still even 

 in this respect the Bracklesham group exhibits features more marked 

 than the London Clay. Amongst the LamellihrancMata of the latter 

 there are but few genera which are not of older date, 26 out of the 

 3 1 commencing in the Cretaceous or Oolitic series ; in the Brackle- 

 sham Sands there are m addition to these 4 more Tertiary and 15 

 older genera. Amongst the Gasteropoda there is a far larger in- 

 troduction of new genera ; for of the 44 genera in the London Clay, 

 16, and of the 59 genera in the Bracklesham Sands, 27 make their 

 first appearance in the Tertiary period. The common occurrence of 

 Cephalopoda is a feature to be noticed. 



With regard to the distribution of the species in the tertiary strata, 

 if we take the 56 species of the lower London tertiaries, in addition 

 to the 224 species of the London Clay, we have together 280 species, 

 212 of which do not pass into the overlying strata. Of the 109 

 genera peculiar to the Bracklesham Sands, there are about 11 which 

 do not descend lower in the English series. 



It is doubtful whether there are any extinct genera pecuhar to the 



* Although the abundance of fishes is a very striking feature in the London 

 Clay, it must not be overlooked that these strata may owe much of their supe- 

 riority in this respect to their very favourable mineral conditions; for in the more 

 open, non-concretionary, and coarser arenaceous sediment of the Bracklesham 

 beds and Calcaire grassier, the fishes, owing to their perishable character, might 

 have been removed before they coidd be fixed by fossihfication ; whereas in the 

 fine calcareo-argillaceous sediment of the London Clay, the segregating action 

 of the carbonate of lime, setting in as soon as the fish-remains became imbedded 

 ill the sediment at the sea-bottom, would quickly and eft'ectually stop the progress 

 of decay, by enclosing them in those concretionary masses of argillaceous lime- 

 stone in which they are now chiefly found. 



