. NATUEE AND OCCUKEENCE 7 



The Foraminifera present many features of 

 interest from a zoological point of view, for they 

 exhibit in certain of their families so complex a shell 

 structure that it seems quite marvellous that the 

 perfect details of their investment have been pro- 

 duced by so lowly a type of animal life, in itself 

 apparently so structureless. The great variability of 

 the numerous types and so-called species of the Fora- 

 minifera, and the inter-relation of genera which at 

 first sight are apparently distinct, lend additional 

 interest to the study of the group. 



Apart from their zoological interest, however, the 

 remains of Foraminifera found in the various fossili- 

 ferous strata of the earth's crust are often of great 

 importance to the stratigraphical geologist, since they 

 assist in determining the age of a deposit, in many 

 cases helping to clear up doubtful points regarding 

 the conditions under which a particular bed was laid 

 down. It must not, however, be inferred that species 

 or types of Foraminifera are always distinctive of 

 special geological horizons, for some well-marked 

 forms are persistent (with some slight modifications 

 in their shell structure) throughout nearly all forma- 

 tions from early palaeozoic times to the present day. 

 But when we study a facies or assemblage of these 

 fossils from any given horizon we find it presents 

 certain peculiarities which distinguish it from that 

 found in another set of strata of a different age. A 

 change in the aspect of a foraminiferal facies may 

 also point to a change of condition under which the 

 animals lived rather than to any great difference in 



