A MONOGRAPH 



BRITISH TERTIARY BRACHIOPODA. 



PRELIMINARY REMARKS. 



The Tertiary Deposits, so rich in fossil remains of most classes of the Animal Kingdom, 

 are remarkably poor in Brachiopoda, few species having lived at that period, especially 

 when compared with the multitude of forms that filled the Cretaceous, Oolitic, and 

 Palaeozoic seas ; the whole class having singularly diminished in number after the 

 cretaceous period up to the present day; for, out of from fifty to sixty recent species, only 

 five are found alive near 010* shores. 



Our supercretaceous strata is principally made up of a vast assemblage of clays, sand 

 and sandstones, gravel and limestones; succeeding and alternating with one another, and 

 sometimes acquiring great thickness and extent. The division of these strata into distinct 

 periods has been the study and aim of many of our most eminent Geologists, who generally 

 seem disposed to admit three principal divisions, as follows: 



/'Upper . . . Superieur . . . (Pliocene of Sir C. Lyell.) 



Tertiary Formations < Middle . . . Moyen . . . (Miocene „ „ ) 



(^Lower . . . Inferieur . . . (Eocene „ ,, ) 



But the exact limits of these have not, in our opinion, been completely established. Some 

 authors object to the use of the terms Eocene, Miocene, and Pliocene, and M. D'Orbigny 

 in particular, in a small work he has lately published, 1 wherein he proposes to replace 

 Sir Charles Lyell's names by those of — 



1 'Cours ele'mentaire de Pale'ontologie et de Geologie Stratigraphiques,' Premiere Partie, p. 260, 18/iO ; 

 and 'Prodrome de Palseontologie Stratigraphique Universelle,' vol. i, Introduction, p. xliv, 1849. 



