on the Organic Composition of Chalk and Chalk Marl. 393 



Sicily with that given by Rozet of the coast near Oran, we 

 cannot avoid recognizing a similarity of relations ; and the 

 thinly laminated marly beds with impressions of fishes, 

 between Caltasinetta and Castrogiovanni, which Hoffmann 

 refers with certainty to the chalk formation, correspond to the 

 similar beds which occur near Oran, but which were said to 

 be tertiary. And the parallel is confirmed by the micro- 

 scopic siliceous Infusoria and calcareous animalcules which I 

 have discovered in both. 



The genera and species of the siliceous Infusoria in Sicily 

 are so similar to those of Oran and Zanle, that of thii*ty-six 

 species, four occur in all the three countries, three in Cal- 

 tasinetta. and Zante, seven in Caltasinetta and Oran, while in 

 all of them the Coscinodiscus Patina is greatly predominant. 

 Of all these siliceous animals, not a single species has been 

 found in the chalk of the North of Europe, nor even in the 

 flints. On the other hand, the calcareous-shelled animalcules, 

 which in the South of Europe accompany the siliceous ani- 

 mals, comprise about one half of the same species that are 

 found in the North, yet exceeding them in quantity. 



From the examination of the organic constituents of the 

 chalk marl we learn the hitherto unknown fact, that nume- 

 rous swarms of microscopic Infusoria were in existence within 

 the period of the secondary formation of the earth's surface, 

 chiefly belonging to such as possess siliceous cases or shells, 

 and which for the greater part are members of such sections 

 of the Bacillaria family as had previously appeared to be con- 

 fined to the tertiary or newest formations. 



Of the thirty-nine or forty species of siliceous Infusoria 

 occurring in the chalk formation, thirty-four or thirty-five 

 have not hitherto been found in the recent state ; but it is re- 

 markable that the remaining five or six species so closely 

 resemble existing species of the present day, that they present 

 no peculiar character by which they could be distinguished 

 from them, and hence the application of new names appeared 

 inadmissible. They are, Eunotia zebra, Fragilaria rhab- 

 dusoma, F. striolata F, Gallionella aurichalca, Navicida ventri- 

 cosa, Synedra ulna*. 



In the chalk itself only four out of the thirty-nine or forty 

 species of siliceous Infusoria liave hitherto been met with, 



* The indifference shown to climate by Infusoria, and the peculiarity of 

 their organic development, seem to render it possible that they might be 

 more readily preserved through many catastrophes of the earth than othcir 

 forms. Ijy the faculty which tlicy possess of spontaneous division, a single 

 individual can, under very favourable circumstances, be multiplied in tiie 

 course of a few hours to the extent of niiilions. 



