1895. OCEANIC DEPOSITS ANCIENT AND MODERN. 275 



3. Those that pass upwards into zones higher than those of the 

 Lower Grey Chalk are precisely those which at the present day have 

 a wide distribution at depths exceeding 500 fathoms. 



4. The more shallow-water types of these ancient species occur 

 together at the present time, in certain well-defined areas, notably off 

 the West Indian Islands, and between Australia and the Papuan 

 Islands. 



5. These regions are characterised by insular development, sub- 

 tropical climate, and are situated, in the wide sense of the term, on 

 the eastern side of a continental area. 



6. We therefore infer that the conditions were similar during 

 Chalk Marl times, greater depression and climatic change causing 

 alterations in physical conditions, and, consequently, variations in 

 the characteristic fauna. 



Bulimines are no exception to the sequence here laid down, for, 

 commencing in the Chalk Marl as very coarse-tested forms, they 

 diminish in size, until in the Belemnitella plena zone, at the base of the 

 Middle Chalk, only very minute examples are as a rule met with. 

 Their species, however, not being comparable, I have not included 

 them in this discussion. Notwithstanding, these also have a region 

 of maximum development ranging between 345 and 675 fathoms, and, 

 although beyond these limits a single, or at most two, species rnay 

 occur in any one sounding, the fact of the genus having been found 

 no less than eighteen times beyond the 700-fathom limit in no way 

 invalidates the general principle presented in no. 3 of the summary. 



Certain exceptional conditions are, however, to be met with, 

 presenting facts of great interest, and well worth consideration and 

 study. 



Thus, in the Taplow Chalk, in the centre of one of the highest 

 zones of tb.e Upper Cretaceous, a number of these forms reappear. 

 This chalk is now generally accepted as a current-formed deposit, 

 and, consequently, the Foraminifera of our Chalk Marl must have 

 been in existence in another part of the Anglo-Parisian Basin, only 

 requiring favourable conditions to enable them to extend their range ; 

 while current agency, as I hope to show in subsequent remarks, has 

 had a great influence in determining local distribution. 



From evidence of a hthological character, it appears probable 

 that the above-named fauna retreated in Upper Chalk times to France, 

 and was existing there in much shallower water, it being a noticeable 

 fact that those species of Textulayia which occur in our Lower Chalk 

 (Cenomanian) are described by D'Orbigny, not from these lower beds, 

 but from the Upper Chalk (Senonian). 



In the Proceedings of the Geologists" Association (xiii., p. 370, Nov., 

 1894), ^Ii"- Chapman has recorded the Foraminifera from the Chalk of 

 Swanscombe. Fifteen of these species, including such ubiquitous 

 forms as Rotalia soldanii, Pulvinulina micheliniana, Cvistellaria cnltrata, as 

 also types of Glohigerina, Anomalina, Tmncatulina, Bolivina, and Bulimina, 



u 2 



