Mr. Webster on the Strata lying over the Chalk. 201 



In the stratum of blue clay, next to the deep red clay that adjoins 

 the chalk of Alum bay, there are septaria with fossil shells, among 

 which I found cytherae and turritellas ; the rest were too much mu- 

 tilated. Hence it would appear, that no fossil organic bodies are 

 disseminated through the pure plastic clays of either basins, but that 

 they are to be found in such beds of this clay as are impure. 



A species of imperfect coal also occurs in the lower strata of the 

 Paris basin, and is probably analogous to that of Corfe, Alum bay,, 

 and Newhaven. 



The French sands are of a great variety of colours. The sands of 

 Alum bay may correspond to that between their chalk and the plastic 

 clay, which is described as very pure, though often coloured red or 

 blueish giey. It is refractory, and often in very large grains. 



In the lower marine formation of the Paris basin, the most re- 

 markable and best characterized stratum is that of the coarse shelly 

 limestone or calcaire grossier. This is generally separated from the 

 chalk by the clay and the sand just described ; or, when that is 

 wanting, it rests immediately upon the chalk. It is sometimes, also, 

 separated from the clay by a bed of sand, more or less thick, in 

 which no shells have been found. 



The description given by the French of this calcareous forma- 

 tion is extremely precise, and corresponds to its importance. From 

 this it appears to be composed of alternate beds of limestone, more 

 or less hard, of argillaceous marl, (;f laminated clay, in very thin 

 beds, and of calcareous marl. These are of great extent, and 

 preserve constantly the same order of superposition, although all 

 the beds are not continuous. Each bed is also characterized by 

 its peculiar fossils. The lower are often more sandy than cal- 

 careous, and when solid they fall to pieces on exposure to the air. 

 They frequently contain a considerable quantity of green earth. 



Vol. II. 2 e 



