337 Tertiary Foraminifera 43 



Summary of Results. 



The difference in size between the Cretaceous and Tertiary 

 Foraminifera is very marked, scarcely any of the latter approach- 

 ing the former in size. Whether this difference is due to the 

 unfavorable conditions for foraminiferal life or because of a dif- 

 ference in the forms of the Foraminifera is not altogether clear; but 

 it seems quite probable that it is due to the greater amount of 

 muddy sediment which is found in the Tertiary beds as compared 

 with the almost pure greensands of the Atlantic Cretaceous. 



This difference in sediment points to more shallow water in 

 Tertiary than in Cretaceous time. Greensand at the present day 

 is being deposited at moderate depths in the Gulf of Mexico as 

 was shown by Pourtales. From the investigations of Murray 

 and Renard and others it is sufficiently proven that the produc- 

 tion of glauconite seldom takes place at depths greater than 900 

 fathoms, and generally occurs from 100 to 200 fathoms. This is 

 necessarily the case since usually the greater depths are found 

 too far from the land to allow inorganic materials to reach the 

 place where glauconite would otherwise be deposited, and it has 

 been shown that this inorganic matter in essential for the for- 

 mation of glauconite. This difference in depth is further sub- 

 stantiated in the Eocene by the great abundance of the shallow 

 water form, Pidvimilina elegans; and the absence of its relative, 

 Pidviiiulina partschiana, which is regarded as a deep water 

 species. 



Among the most chara(5leristic genera of the forms identified 

 as belonging particularly to the Eocene may be mentioned 

 Amphistegma. The genus Nodosaria is represented by only five 

 species none of which are abundant. Cristellarians are also ap- 

 parently very scarce in the Eocene while the genus Polymorphina 

 has a wide representation. The genus Cyclammina is of excep- 

 tional interest inasmuch as it is considered by Prof. H. B. Brady 

 to be unknown in the fossil state, but that it occurs in beds of 

 Miocene age in New Jersey is proved beyond question by the 

 author who has given the specimens a careful and thorough 

 study. 



The shell is finely arenaceo-siliceous and hence is unaffecfted by 

 acids. Its structure is peculiar and quite complex which, together 



