169 



the completion of one fitraturn and the commencement of another, 

 to allow the lower one to become comjjact. I'he irregTalaritie.H of the 

 flints are always on the upper side ; one seam in a pit near Merrow 

 consists entirely of the silicified remains of A nunc ky tea. These were 

 evidently ail dead crusts which had lost their spines before they were 

 drifted over the bed where we now find them. I'his species however 

 is not confined to such layers, but is found in extraordinary numbers 

 in each separate bed ; and in another instance an AHlrata had time 

 to spread itself out over the surface. 



Considering the small number of animal remains we yet possess 

 from the chalk formation, when viewed with reference to its vast 

 thickness, there being not more than four or five species to 100 feet, 

 5t seems hazardous to refer the whole of this wide-spread mass of cal- 

 fiareous matter to the destruction of animal structures ; but the im- 

 pression constantly produced by a microscopic examination of the 

 white cUalk in every place has been, that it was the deep sea deposit 

 of a wde ocean, which in parts teemed with animal life, but of which 

 the localities have long since disappeared in the extensive destruction 

 which it has everywhere experienced ; and that all we have to judge 

 from is such portion as was not generally calculated to support animal 

 life, with the exception perhaps of Foraminifera and Brachiopods : 

 the specific gravity of shells and corals is in favour of the wide dis- 

 tribution of their materials when pounded. 



Nor is this purely hypothetical : there are some remarkable beds 

 a little below that portion of the deposit last described which bear 

 it out : they are beds which were a])parently deposited when the 

 waters could drift rather coarser materials than usual ; so that the 

 ■greatest portion consists of broken branches of corals, shells and 

 Echinoderras, cemented by the usual comminuted matter of the or- 

 dinar}' chalk strata. Escharu cancellata, E. pyrif'/rmvi , Cdlepora hl- 

 punctata, Cerioporu madreporacea, Retepora trancata, Harpvla. plexva, 

 and Cidaris vesiculosa are the principal species met with. 



For a ver}" considerable depth below thLs, through that portion 

 -where the seams of flint are most regular, it is almost in vain to 

 .search for any traces of animal life. This condition of things is con- 

 tinued downwards as far as the chalk without flints, where Inocffra- 

 mus myiiloides and euvieri, Lima hyperl, Plarjiostomoi and Te-rehratula, 

 Taecome abundant, together v/ith the remains of fishes ; and which 

 beds are succeeded by others which afford a grey limestone, and con- 

 tain Ammonites rhotomagensis , A. mantelli, A. lewesiensis, A. varians, 

 Turrilites tv.herculo.tu3, Scaphites aqualis, Pecten heavfrri, and Anan- 

 chytes rudiatus. 



This lower chalk, which through a considerable thickness had 

 heen gradually becoming more compact, thick-bedded and dark-co- 

 loured, suddenly changes to a rock, exactly resembling the upper 

 white fragmentary beds. This portion cf the series, taken in a de- 

 scending order, slowly acquires an admixture of sand and green 

 earth, so as to become first a craie chlorit4e, till by the farther di- 

 minution of the calcareous matter we reach the bright green beds of 

 the upper greensand with Plicatula inflata : below these strata of 



VOL. IV. PAET I. N 



