GEOLOGICAL EANGE 267 



ceeding beds, but they have been sho^Yn to contain 

 a considerable number of distinct forms. 



The ' Chalk rock ' or zone of Holaster i^lanus is 

 in England largely constituted of Foraminifera 

 (see fig. 4), principally Textularia (jlohulosa and 

 Glohigerina crefacea and rnar(jiiiata, and it is here 

 we seem to obtain a first glimpse of the different 

 and varied microzoic fauna so characteristic of the 

 Upper Chalk. 



The ' Micraster Chalk, with flints,' is in most of 

 its zones largely constituted of foraminiferal shells, 

 and some forms, like Textularia glohulosa and 

 Bolivina strigillata, are especiall}^ characteristic of 

 this part of the series. At certain levels the chalk 

 is partly replaced by phosphate of lime, and this 

 mineral change, to a great extent, has the effect 

 of preserving the shells. The flints of this series, 

 when hollow, are found to contain a siliceous powder, 

 sometimes called 'Flint-meal,' which is largely made 

 up of the casts or replacements of Foraminifera and 

 other organisms, such as Ostracoda, polyzoa, and 

 also sponge-spicules. The following species, among 

 others, are characteristic of the Upper Chalk fauna, 

 including those mentioned above : Textularia 

 decurrens, T. serrata, Gandrgina Jo)ie,siaii(i, Mar- 

 ginulina elongata, CrititeUaria Gaudrgana, Flahellina 

 rugosa, F. ornata, F. Baudouiniana^ Folgmorphina 

 acuminata, Truncatulina Clementiana, T. Lorneiana, 

 and Botalia exsculpta. 



The White Chalk of the Island of Eiigen has 

 been productive in Foraminifera, and Marsson has 



