on the Organic Composition of Chalk and Chalk Marl. 391 



On the Chalk Marl, and its relations to the Chalk and its 

 Flints. 



The whole coast of Oran in Africa appears to belong to 

 the chalk formation, composing the plain east of the town, 

 and extending thence to the Atlas. The marl brought from 

 thence as tertiary by M. Rozet in great quantities I had an 

 opportunity of examining in Paris, and I found not only Po- 

 lirschiefer and an Infusoria conglomerate, but calcareous ani- 

 malcules of the same species as occur in the chalk of Poland, 

 Riigen, Denmark, and Paris, and which there mainly contri- 

 bute to its mass. It thus appeared that the so-called tertiary 

 formation of the coast of Barbary might, without much hazard, 

 be brought into a nearer connexion with the chalk. In his 

 description of this tract, M. Rozet states*, "The tertiary 

 formation is extensively developed in Oran, forming the soil 

 of the large plain on the east of the town, and on the south 

 to the Atlas. It forms also the sea-coast to an extent of 3000 

 metres between Mers el Kebir and Cape Falcon, and the 

 whole soil of the adjacent plain. The lower bed is a blue 

 marl, like that which we found at Algiers and within the Atlas. 

 It appears destitute of organic remains. The second or upper 

 deposit consists of marly and calcareous beds in alternation, 

 forming a thickness of 30 to 40 metres. In the plain these 

 beds are apparently horizontal, as well as in the elevated plain 

 of the Rammra hill; but in the hills south-west of the town 

 of Kasba they are, on an extent of two hours march, inclined 

 to the north, at an angle sometimes exceeding 30°. The beds 

 of limestone are white and chalk-like, yellowish and coarse 

 granular, usually forming the lower part, succeeded by others 

 alternating with yellow marls, which are often slaty and 

 charged with sand, and between them are found layers of 

 ostreae and other shells. Among them two beds are distin- 

 guished, each one metre in thickness, composed of very white 

 finely-laminated marl, containing numerous well-preserved 

 impressions of fishes, so that in a cubic mass of one foot we 

 seldom fail to find three or four fishes. In these beds of marl 

 thus enclosing the fishes, other organic remains do not appear; 

 but in the calcareous and sandy beds which intervene, occur 

 layers of large oysters mingled with grypheae. The upper 

 part of this deposit is composed of a calcareous breccia, which 

 is exhibited at the surface in the soil of the whole plain on 

 the south-west of Oran." 



This exact description of the position and thickness of the 

 white marl with impressions of fishes, has a reference to the 



* Rozet, Voijage dans la R^gencc d" Alger, Paris, 1833. tome 1. chap. v. 

 pp. 56, 63. 



