1844.] 409 



A. The lower assemblage of clays, mostly fullers' earth, abound- 

 ing in fossils, and in which the Perna sand-rock and the Cracker 

 nodules are exceptional strata, indicating temporary conditions. 



B. The region of Gryphma sinuata sands, in which the Tere- 

 bratula bands and upper clays are exceptional strata. This region 

 may be subdivided into three portions, the two lower containing 

 Crioceras nodules separated by the clay, and the upper containing 

 no nodules. The noduliferous part of the series, and that which is 

 free from the nodules, have each a zone of TerebratulcB for a base. 



C. The region of ferruginous sands, which may itself be divided 

 into two or three sections, the lowest of which is fossiliferous. 



§ 3. Chemical Peculiarities of the Beds. 



A chemical analysis of the composition of the several strata was 

 next given ; the principal results of which, affecting the distri- 

 bution of the organic remains, are the following : — 



The beds which are most fossiliferous are those containing most 

 carbonate of lime. In the ferruginous beds, whether upper or 

 lower, there are no traces of lime ; but large quantities of peroxide 

 of iron. This is true as well of the fossiliferous as the non-fos- 

 siliferous parts. The gault which caps the iron bands at Black- 

 gang- Chine contains but few fossils, and those occur rarely. On 

 analysis it was found to exhibit no trace of carbonate of lime, but 

 a little gypsum ; whereas the fossiliferous gault of Folkstone and 

 other places abounds in carbonate of lime. 



§ 4. Indications of Conditions under which these Beds were deposited. 



At the close of the deposition of the "Wealden, there appears to 

 have been a sudden depression of the bed of the great freshwater 

 estuary, and an influx of the sea. The first effect of such an 

 influx would be the destruction of the animals in the estuary not 

 adapted for living in salt water ; hence we find a total destruction 

 of the Wealden animals, the remains of which accumulate towards 

 the point of the junction of that formation with the Lower Green- 

 sand ; a fact which indicates the nature of the change. Even the 

 Cerithium, although belonging to a genus many species of which 

 are capable of living in the depths of the sea, was destroyed — not- 

 withstanding that its appearance, only in the uppermost beds of the 

 Wealden, indicates that its presence there was due to the com- 

 mencement of the very state of things which eventually destroyed it. 

 That the depression was of some extent, though not, pei"haps, of very 

 many fathoms, is indicated by the nature of the animals which lived 

 in the first-formed sea-bed, and which, when they died, were often 

 imbedded in the fine and, probably, fast depositing mud, in the 

 vertical position which it is the habit of the animals of such genera 

 as Pinna and Panopcea to assume when alive. After this, a tem- 

 porary change followed, when an influx of sand, mingling with 

 the calcareous mud, caused a state of sea-bottom peculiarly fa- 

 vourable to the presence of animal life. In this way were called 



H H 4 



