178 RELICS OF PRIMEVAL LIFE 



from very old geological formations are often scarcely 

 distinguishable from those now living, and must have 

 played precisely the same parts in the system of 

 nature. One of these functions is that of accumu- 

 lating great thicknesses of calcareous matter in the 

 sea-bottom. 



The manner in which such accumulation takes 

 place we learn from what is now going on in the 

 ocean, more especially from the result of the recent 

 deep-sea dredging expeditions. The Foraminifera 

 are vastly numerous, both near the surface and at 

 the bottom of the sea, and multiply rapidly; and 

 as successive generations die, their shells accumu- 

 late on the ocean bed, or are swept by currents 

 into banks, and thus in process of time constitute 

 thick beds of white chalky material, which may 

 eventually be hardened into limestone. This pro- 

 cess is now depositing a great thickness of white 

 ooze in the bottom of the ocean ; and in times 

 past it has produced such vast thicknesses of 

 calcareous matter as the chalk and the nummulitic 

 limestone of Europe and the orbitoidal limestone 

 of America. The chalk, which alone attains a 

 maximum thickness of 1,000 feet, and, according 

 to Lyell, can be traced across Europe for 1,100 



