%;■ OCEANIC DEPOSITS ANCIENT AND MODERN. 27: 



parison, it may, at first sight, appear that the existence of any 

 uniformity in faunal character in the two cases must be absolutely 

 impossible. The period of time which has elapsed should have been 

 sufficient to alter and vary every specific type, and obscure any 

 relationship which might help to guide the student. Such pre- 

 conceptions, however, break down at the very outset, and though as a 

 rule in the higher Vertebrata and MoUusca only generic resemblance 

 can be traced and compared, yet in the lower forms of life, more 

 especially among the Foraminifera, the identity of specific character 

 becomes striking and significant. 



The first analysis of a sample of Chalk Marl carried out by me 

 brought the matter very prominently under my notice ; for after the 

 removal of all the clayey and calcareous material, an insoluble and 

 heavy residue remained, which revealed itself as being largely made 

 up of the tests of arenaceous Foraminifera. 



A comparison of these with recent forms showed that most of the 

 species still exist at the present day. This resemblance would be of 

 little value if the same types were simply distributed far and wide in 

 the oceanic waters ; but if it can be shown that only certain localities 

 are specially favoured, reasons should be sought to explain the 

 occurrence. 



Three Textnlavia (T. tiirris, T. trockus, and T. agglutinans) occur in the 

 Lower Chalk Marl. Only at Culebra Island, in the West Indies, at 

 a depth of 390 fathoms, do these same three species occur together at 

 the present day ; one of them, T. tuyris, has only been met with here 

 and off Pernambuco, at a depth of 350 fathoms. Three species of 

 Vevneiiilina have been determined by Mr. Chapman from the Taplow 

 Chalk {V. pygm^a, V. spinulosa, and V. triquetra); these same three 

 species have also been met with at Culebra Island, and nowhere else do 

 they occur together. Gaiidryina pupoides, Bulimina presli, Haplopliragmium 

 latidorsatuni, a.nd A iiunodiscus incertus all occur in the Chalk Marl. They 

 are also present at Culebra Island. I am in a position to still 

 further multiply the cases of identity between the two, but these 

 coincidences should be sufficient to give rise to careful thought. 



Which, then, represents the line of logical hypothesis ? Is it the 

 conception that, on'ing to accidental circumstances, all these ancient 

 specific forms have become associated unchanged in certain restricted 

 areas ? or, is it that identity of circumstances has led to their 

 preservation, and to the similarity of distribution they display both in 

 the Cretaceous deposits and at the above-mentioned localities at the 

 present day ? 



What, then, do these circumstances appear to be ? It will be 

 noticed that Culebra Island possesses the following distinctive 

 characteristics. It is situated close to the eastern boundary of a 

 continental area, in a region of considerable insular development, 

 having a sub-tropical climate, and not far removed from the fine of 

 a great current. 



