236 



are identical with the representative of the argiles glauconieusea 

 of the Bonlonais, or Middle Portlandien. The Portland sand 

 of Fitton comprises the "sables glauconieux," which correspond 

 to the "couches sablenses et glauconieuses" of the upper portion 

 of the Middle Portlandien of the Boulonais; these sands 

 contain, at Shotover, the same fossils as the sub-adjacent clay 

 of Hartwell, and are related like the beds with Astarte 8cemanni 

 of the Boulonais to the Middle Portlandien. The upper 

 portion of the sands, without the silicate of iron, Glauconite, 

 are destitute of fossils, these M. S^mann unites with the 

 Portland stone, and groups as Upper Portlandien. The sands 

 are overlain by a bed with Cardium Pellati, which contains at 

 Swindon Perna Bouchardi, and at Hartwell Pecten lamellosus 

 and Ostrea ex^ansa. At Swindon this bed is covered by a hard 

 blueish rock, containing Ammonites giganteusj above this are 

 twenty feet of sands with inconstant layers of sandstone, and 

 some beds containing Trigonias intercalated with them. The 

 sands are overlain by a series of Limestones and marly 

 sediments, in the lower portion of which we find Gerithimn 

 Portlandicum, corresponding to the great horizon of the Island 

 of Portland, and in the upper portion Lucina portlandica, 

 Cyrena rugosa, and Neritoma sinuosa. 



If this reading of the Hartwell section is correct, the con- 

 clusion is — 



1st, — That in England the Lower Portlandien, or the beds 

 with Perna rugosa and Pterocera Oceani, is absent. 



2nd, — That the Middle Portlandien is represented by the dark 

 sandy clays of the brickyard at Hartwell, containing Ammonites 

 hiplex, Cardium Morinicum, and Ostrea expansa, &c. A portion 

 likcAvise of the overlying fossiliferous sand, with green Glauconite 

 grains, belongs to this group. 



3rd, — The Upper Portlandien, so largely developed in England, 

 has at its base the non-fossiliferous sands without Glauconite, 

 and in its middle and upper portions the true calcareo-siliceous 

 Limestones and other beds forming the Portland stone, and 

 containing Ammonites giganteus, Cerithium portlandicum, Natica 

 elegans, Natica Ceres, Trigonia incurva, Trigonia gibbosa, Cardium 

 dissimile, Pecten lamellosus, &c. 



