8 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA 



their comminuted and dissolved remains subsequently reprecipi- 

 tated. 



Certain zones of the Chalk, notably the zones of Holaster planus 

 and Micrdster, yield Foraruinifera in larger numbers, but even 

 here a section of the rock will show their limited distribution^ 

 The bulk of the organic remains will be found to consist of small 

 spherical bodies which when cut in section show as rings (PI. 2 r 

 fig. 1). These, the so-called " Spheres " of the chalk, are perhaps- 

 the origin of the belief that chalk is built up of the shells of 

 Foraminifera. But whatever the " Spheres " may be, we are 

 convinced that they are not Foraminifera. Their nature is still 

 in doubt, although they have been relegated in turn to the 

 Foraminifera, the Radiolaria and the Diatomaceae. Mr. W.. 

 Hill, F.G.S., of Hitchin, whose knowledge of the microscopic 

 structure of chalk is unrivalled, and who has devoted many years- 

 to the study of these " Spheres," has published a scheme for the 

 division of the Chalk into zones, based on their occurrence and 

 numbers (32), but he is still unable to explain their origin and 

 nature. We suggest that they may be the chitinous tests 

 Of flagellate infusoria such as are found in great numbers in the 

 sea to-day, of practically identical size and shape. 



The Chalk of Maestricht is rich in Foraminifera, and may 

 be regarded as the starting-point of the rich Foraminiferal 

 fauna of the Tertiary period, as it contains many large genera r 

 OrbiioliUs, Operculina, Orbitoides, etc.> which reached a maxi- 

 mum of development and distribution in Eocene and Miocene 

 times. 



Passing into Tertiary times we reach the Golden Age of the 

 Foraminifera; the age in which they were to reach their 

 maximum development both as regards size and abundance, and 

 to leave their remains in great beds extending across whole 

 continents, and often of an enormous thickness. 



These Tertiary Foraminifera are very sparingly represented 

 in Great Britain. The London clay, although it contains a rich 

 rhizopodal fauna in a limited zone, is on the whole absolutely 

 barren, and the Thanet Sands and Woolwich and Beading beds 

 have yielded few records. 



In the Bracklesham beds of Hampshire, however, we find a 

 zone almost entirely composed of two or three species of Nummu- 

 lites. At Selsey Bill the foreshore at low tide, on the east shore, 



