8 



THE FOEAMINIFEEA 



age, and in such case the earHer aspect of the fauna 

 would return at a later period, provided there did not 

 elapse too great a space of time, when the former 

 marine conditions recurred. 



The Foraminifera have in past geological times 

 been among the most active agents in building up 

 the sedimentary rock masses of the earth, by secreting 

 the carbonate of lime from the waters of the ocean. 



Fig. 6. — Terrigenous (Green) Fig. 7. — Globigerina Ooze, x 24. 

 Mud, with Foraminifera, x 24. North Atlantic, 2,760 fathoms. Original. 

 Off Cape Verde, 284 fathoms. Oricjinal. 



This work is still being carried on by them around 

 the shores of continents, where their accumulated 

 shells go to form, along with the land debris, the 

 terrigenous deposits (fig. 6), and over large areas 

 of the ocean fioor, where, intermixed with coccoliths, 

 they form the well-known Globigerina ooze (fig. 7). 



The organic rocks formed by the agency of 

 Foraminifera are often of very great thickness and 

 extent, and foraminiferal rocks are found inter- 



