I FORAMINIFERA 25 



of the ocean water in the warmer regions of the globe and consequently 

 there is as it were a continuous rain of their dead bodies down into the 

 depths. Sinking down with extreme slowness their shells are all the while 

 exposed to the solvent action of the sea-water and in the deepest oceans 

 they have been completely dissolved long before the bottom, is reached. 

 In waters of more moderate depth however they reach the bottom and, 

 being protected from further solution by the bottom layer of water becom- 

 ing saturated with calcium carbonate, they accumulate in the form of a 



Fig. 9. 



Skeletons of Foraminifera. 



characteristic greyish foraminiferal ooze — called Globigerina ooze from 

 the genus Globigerina (see Fig. 9, uppermost figure) which is one of the 

 commonest of these pelagic foraminifera. Foraminiferal ooze has played 

 an important part in the building up of rocks in past geological ages. 

 If a piece of natural chalk be examined by appropriate methods it is found 

 to consist in great part of foraminiferal shells, though these frequently 

 resemble the shells of shallow-water species of the present time rather than 

 pelagic types. Another rock composed of foraminiferal remains is the 

 remarkable Nummulite limestone of Eocene age which stretches in a 

 belt across the Old World from Southern Europe to ■ Japan. This is 



