140 MESSRS. A. J. JUKES-BROWN E AND W. HILL : [May 1 896, 



chalk has a correspondingly denser texture. In other specimens y 

 especially where sponge-spicules are numerous and there is much 

 colloid silica, the fine and denser material seems to be in isolated 

 grains or patches, and the rock has a granular aspect on its fractured 

 surface. These grains seem to consist of fine calcareous material 

 cemented by colloid silica or amorphous siliceous material. 



The structure of the rock, then, somewhat resembles that seen 

 in Beds 10 and 11 of the Devon Cenomanian, namely, separated 

 calcareous fragments cemented together. The similarity is even 

 carried further by the absence of Globigerince and ' spheres,' and 

 by the comparative rarity of Inoceramus - prisms, while shelly 

 particles, whose derivation is uncertain, abound in both deposits. 



The differences between Bed 6 of La Heve and Bed 1 1 of the 

 Devon series are the abundance of sponge-spicules and colloid silica 

 in the former, and the greatly superior size of the glauconite- and 

 quartz-grains in the latter. Moreover, the rock of Bed 6 never 

 becomes a crystalline limestone, and is usually in a condition which 

 admits of its particles becoming readily detached. 



Hard beds and semi-crystalline lumps do occur, especially at 

 St. Jouin, but nothing in the specimens we brought home, either 

 from this locality or La Heve, completely parallels the granular 

 structure of Beds 10 and 11 of Devon ; in one from Yimoutiers, 

 however, this structure is almost exactly reduplicated. 



The presence of so much quartz and glauconite, the abundance of 

 sponge-spicules, and the absence of Globigerince and spheres seem to 

 show that this part of the Cenomanian was laid down in shallower 

 water and nearer a coast-line than the English Chalk Marl. 



Beds 7 and 8. 



Prom near the base of Bed 7 the rock passes to a deposit which 

 we may compare with our Grey Chalk. It consists of the usual 

 amorphous calcareous matter, in which are scattered small shell- 

 fragments, a few calcareous spheres and foraminifera. Globigerince 

 continue rare. Sponge-spicules occur, but are less numerous, and 

 there is little or no colloid silica. The Chalk at this horizon differs 

 from its English equivalent in the presence of sponge-spicules, and 

 in the occurrence of grains of glauconite and quartz. It is true 

 that minute particles of both these minerals are to be seen far up 

 in the Grey Chalk in the neighbourhood of Warminster and Devizes, 

 but neither are found commonly in the Chalk of the Isle of Wight, 

 which approaches most closely (so far as distance is concerned) to 

 that of Cape La Heve. 



Specimens taken from the base of the Turonian at Brunval show 

 that the Chalk at this horizon is full of ' spheres ' and Inoceramus- 

 prisms, and is similar to that at the base of our Middle Chalk. 



