38 HAMPSTEAD HILL. 



we learn the minimum extent of the sea in which it was de- 

 posited. 



And still more even than this may be learned, from the fossils 

 which are embedded in it, of geographical changes. For, since 

 .they show the kind and character of the organic life of the 

 London Clay sea, so also do they indicate clearly to us the 

 general climatal conditions of the area of the sea ; or, in other 

 words, they tell us whether the sea was a warm one or a cold 



one. 



The London Clay furnishes an abundant and interesting fossil 

 Fauna, and a less abundant but still interesting fossil Flora. The 

 fossil Flora, or assemblage of plant remains, is almost exclusively 

 confined to the Isle of Sheppey area, where large quantities of 

 fruits have been found fossil. The fruits have evidently been 

 similar to those now growing on the banks of tropical rivers, and 

 which at certain seasons almost cover the surface of their waters. 

 Many species have been described by Dr. Bowerbank from the 

 Sheppey London Clay, but the genus best represented greatly 

 resembles the Nipa, so abundant on the banks of the Ganges, 

 and is therefore called Nipadites. The inference from the abun- 

 dance of these remains of land plants in the Isle of Sheppey, 

 and their limitation to that area, is that in that neighbourhood 

 debouched a river, which, after running through lands covered 

 with palms and other tropical vegetation, brought the fruits which 

 had fallen on its surface to the sea, to the bottom of which they 

 in due course sank and so were embedded in the accumulating 

 sediments. 



The fossil Fauna of the London Clay, though abundant, is 

 subject to remarkable restrictions, both as to area and vertical 

 position. Thus the higher Classes, those having backbones, or 

 the Vertebrata, the reptiles and fishes in fact, are almost exclusively 

 confined to the Kentish area, while the distribution of the lower 



