of Cretaceous Bocks. 163 



l-288tli of a line, that frequently there must be far above a 

 million in each cubic inch, and hence far above 10 millions in 

 a pound of chalk. In the white or yellow chalk of the north 

 of Europe, the particles of a somewhat crystalline nature, are 

 equal to, if not greater in amount than, the organic remains, 

 according to the respective volumes of the mass ; but in the 

 chalk of southern Europe, these organisms, and their visible 

 fragments, greatly predominate ; and these consist, as it woidd 

 seem, exclusively of well preserved polythalamite. But when 

 we spoke of a milUon of polythalamiaj in every cubic inch, we 

 include only those which are well preserved, of which the 

 fourth part of a cubic line, or every l-12tli of a grain of chalk, 

 can be ascertained to contain 150 to 200, which would be 

 equal to 600 or 800 in each cubic line, about 1800 to 2400 in 

 each grain, and from 1,036,000 to 1,382,400 in every cubic 

 inch. 



Besides the polythalamic cretaceous animalcules, siliceous 

 infusoria have been found in chalk at Gravesend, near Lon. 

 don.* Professor Ehrenberg has also found the cretaceous 

 animalcules in the polishing-slate from Oran in Africa (ter- 

 tiary marl, according to Rozet), and in the polishing-slate of 

 Zante ; and it has been discovered by him, that even the chalk 

 marl of Sicily, which there forms whole ranges of hills, and 

 which Friedrich Hoffmann recognised as a member of the 

 chalk series, is composed of extremely Avell preserved siliceous 

 infusoria, including several of the characteristic chalk animal- 

 cules. He likewise recognised three specimens of similar chalk- 

 marl, composed of infusory animals, or calcareous polishing- 

 slate, among Greek minerals brought by Mr Fiedler ; and it has 

 been ascertained that many of the siliceous infusory animals 

 of the chalk-marl of Sicily, Oran, Zante, and Greece, are 

 identically the sa)ne, and at the same time do not occur in 

 other localities. i,astly, by an examination of the num.mulito 

 limestone of Cahira, and of the pyramids of Gyzeh, specimens 

 of which he brought with him from ligypt, the author has dis- 



• In the flints of tliat locality tlic antlior also saw distinct scales of fishes, 

 first of all in the collection of Mr Bowcrbank of London ; but lie afterward* 

 liiniself found f>iiniiar siMxiiuens, which liv carried home witii him. 



