FORMATIONS ABOVE CHALK. 311 



folk. In other places, as at Sheppey, Erasworth in Sus- 

 sex, &c. vast quantities of the fruits of tropical countries 

 have been found in a corresponding situation. 



3. Upper Marine Formation. 



This bed consists of bluish or greenish marl and clay, 

 containing a great number of fossil marine shells, which, 

 in general, are different from those found in the London 

 clay. It is known in this country, with certainty, only 

 in the Isle of Wight; 



4. Lower Fresh Water Formation. 

 This formation is ascertained in the Isle of Wight. 

 It is placed under the last, and consists of clay, marl, 

 and sand, with vegetable matter resembling an imper- 

 fect coal, or peat, and contains numerous fragments of 

 fresh water shells. At the bottom is formed a mixture 

 of marine with fresh water shells. As the alternation of 

 marine with fresh water strata has not been observed in 

 any other part of this country, except the Isle of Wight, 

 the traces of a fresh water formation in the London ba- 

 sin cannot perhaps be referred to this. 



5. Sand without Shells. 



In the Isle of Wight this sand is extremely pure ; it is 

 dug at Alum Bay, and is used for making the best glass. 

 The Bagshot Sand, perhaps, belongs to this ; and possi- 

 bly the Gray weathers ; but the position of these has not 

 yet been accurately determined. 



6. London Clay. 



This is the blue clay of London, Highgate, Sheppey, 

 Portsmouth, Stubbington, Hordwell, Southend, Harwich, 

 &c. It is distinguished by its septaria, and its beautiful 

 and numerous organic remains. In Alum Bay it is the 



