THE CHALK FORMATION. 



307 



and veins of flint occur in the lowermost beds of white 

 chalk. The inferior members of this formation, the Fire- 

 stone, Gait, and Greensand, are constant in their characters 

 and relations, in England, and over a great part of the Conti- 

 nent of Europe : the following is a concise view of these 

 deposits, in connexion with the upper group. 



Upper Chalk. 



Lower Chalk. 



CHALK FORMATION. 



Strata of white limestone, 

 with parallel layers of 

 siliceous nodules, and 

 veins and tabular masses 

 of flint. Chalcedony; Calc- 

 spar. Pyrites j quartz 

 pebbles. 



Strata of white limestone ; 

 calc-spar, pyrites, seams 

 of marl j quartz pebbles ; 

 flints very rarely. Lower 

 beds often grey and argil- 

 laceous. 



Marine shells : Ammo- 

 nites, Nautili, Belem- 

 nites. Crustaceans ; 

 Echinoderms ; Star- 

 fish. Fishes. Bones of 

 Mosasaurus, Ichthy- 

 osauri, Plesiosauri, 

 Turtles, and other 

 reptiles. Corals, Spon- 

 ges, and other zoophy- 

 tes. Fuci; drift-wood; 

 Cycadeous plants. 

 Almost all the genera 

 and species extinct. 



Firestone. 



Beds of marl, passing into 

 calcareous sandstone and 

 sand, full of green parti- 

 cles {Firestone). Bands 

 of hard sandy and cherty 

 limestone. Pyrites; chal- 

 cedony; often forming the 

 casts of shells. 



Shells, &c. as in the 

 chalk ; but many spe- 

 cies peculiar. Cepha- 

 lopoda more abun- 

 dant and diversified. 

 Chimaeroid and other 

 fishes Some layers 

 abound inmolluskite. 



Gait. 



Dark blue clay and marl, I 

 with thin layers of red ) 

 marl ; gypsum ; pyrites. L 



x 2 



^ Ammonites, Hamites, 

 I Belemnites,and other 

 cephalopoda : many 

 species peculiar. Se- 

 veral characteristic 

 shells and crustace- 

 ans ; drifted conife- 

 rous wood. 



