104 Dr. FiTTON on the Strata below the Chalk. 



In stating the result of this investigation^ I shall give a series of sections of 

 the strata below the chalky at places which I have myself examined *, beginning 

 on the coast near Folkstone, and following the outline of the chalk thence to 

 the sea on the N. West of Norfolk. The relative situation of these places is 

 shown in the map annexed to this paper f. The intermediate country, in 

 general^ I have not examined in detail, and some points of importance I have 

 never seen; but those who may have opportunities of continuing the inquiry, 

 will find, I hope, no difficulty in connecting their observations with mine. 



(3.) The series of strata about to be described extends from the Chalk down 

 to the Oxford oolite or coral-rag, and is composed of alternating but irre- 

 gularly distributed beds of Sand, Clay, and Stone. 



Among the sandy strata, it is important to discriminate not only between the 

 Lower green-sand and that of Hastings, but to distinguish both from a third 

 group, consisting principally of sand abounding in green particles, which lies 

 beneath the Portland stone. 



Clay, of several varieties, occurs in all parts of this series; but three groups, 

 constituting the Gault, the Weald-clay, and the Kimmeridge-clay, derive pe- 

 culiar importance from their generally occupying valleys, or depressions, at 

 the foot of the escarpments of the Chalk, the Lower green-sand, and the Port- 

 land stone, respectively, and thus producing conspicuous natural features in the 

 tracts where this succession is observable. 



The stone of the tracts under consideration is either limestone; indurated 

 sand-rock; chert; or siliceous matter intimately mixed with carbonate of lime, 

 in the form of grit, — which has commonly a concretional structure, and seems 

 to pass into continuous beds only by the approach and ultimate union of the 

 concretions. 



But the most remarkable distinction, in the suite described in this paper,arises 

 from the great difference of character in the organized remains which the 

 principal groups include. The fossils of the chalk and green-sands and those 

 of the Portland stone, are all marine, and the species numerous. But in the 

 Wealden, between the lower green-sand and the Portland stone, although the 

 fossils are abundant as to quantity, the species are comparatively few, and by 

 far the greater part of them belongs to fresh water. The whole of the phe- 

 nomena, in short, presented by this remarkable assemblage of beds, are such 

 as to accord with the hypothesis of their having been deposited in fresh water 

 communicating with the sea. 



* Plates X. a, and X. b. 



■f- Plate IX. — The detail, upon a larger scale, will appear in the new edition of Mr. Greenough's 

 Geological Map of England. 



