SECT. IT. FOSSIL FORAMINIFERA. 53 



dual animals. In the earlier part of the Tertiary period 

 the Nummulites acquired an extraordinary size. They 

 were like very large coins two or more inches in dia- 

 meter, and were accumulated in such quantities as to 

 constitute the chief part of the nummulitic limestone;"} 

 a formation in some places 1,500 feet thick, which 

 extends through southern Europe, Libya, Egypt, Asia 

 Minor, and is continued through the Himalayan moun- 

 tains into various parts of the Indian peninsula, where 

 it is extensively distributed. The Great Pyramid of 

 Egypt is built of this limestone, which gave rise to 

 singular speculations with regard to the Nummulites in 

 very ancient and even in more recent times. Although 

 this is incomparably the greatest, it is by no means 

 the only instance of an accumulation of the fossil shells 

 of individual animals. The ( Lingula flags,' a stratum 

 in the upper Cambrian series of North Wales, was so 

 named from the abundance of the Brachiopod Lingula 

 that it contains. 



Professor Ehrenberg discovered that the shells of 

 the Foraminifera sometimes undergo an infiltration of 

 silicate of iron, which fills not only the chambers, but 

 also their canal-system even to its minutest ramifications, 

 so that if the shell be destroyed by dilute acid, a per- 

 fect cast of the sarcode matter remains. The green- 

 sands in the different geological strata from the Silurian 

 formation upwards, are chiefly composed of these casts ; 

 and Professor Baily of the United States more recently I 

 discovered that a process of infiltration is even now taking 

 place in some parts of the ocean bed, and that beautiful; 

 casts of Foraminifera may be obtained by dissolving 

 their shells with dilute acid. 



A most extensive comparison of the Foraminiferous 

 group of Khizopods, recent and fossil, has been made 

 by Messrs. Parker and Rupert Jones from almost every 

 latitude on the globe, from the arctic and tropical seas, 



