2S8 PHYSIOGRAPHY. [chap. 



localities, the deposits in question have received their name 

 of Bags/tot beds. It has been already explained (p. 25) 

 that the hills of Hampstead, Highgate, and Harrow are 

 capped by Bagshot sand ; but these areas are too small to 

 be represented on the map. Very few fossils occur in these 

 sands, but those which have occasionally been found are 

 fragments of marine shells, thus showing that the area m 

 which they occur has been, at some time, under the sea. 

 There is little doubt that the Bagshot sands were once spread 

 over a wide surface in the lower part of the Thames basin, 

 and that a great portion of thern has since been removed by 

 deundation. 



Reference to Fig. 7 (p. 26) will show how the Bagshot 

 sand usually rests upon the London, Clay. This clay, which 

 is the next rock in passing downwards from the Bagshot 

 beds, is represented in Plate V. by a dark-brown colour, and 

 is seen to cover a very wide area. It is. for the most part, 

 a stiff brown clay, which has evidently been deposited, as 

 fine mud, upon the bottom of the sea, not far from land. 

 In fact, in the Isle of Sheppey, the clay has yielded a great 

 variety of vegetable remains, some of which indicate a very 

 warm, not to say tropical, climate. Thus the fruit of the 

 Nipadites represented in Fig. 63 (p. 230) has its modern 

 representatives in Bengal and the Asiatic Archipelago. 

 Such relics of terrestrial vegetation indicate that land could 

 not have been far from tlie water in which the clay was de- 

 posited; and the occurrence of the bones of crocodiles also 

 tends to the conclusion that the Sheppey clay represents the 

 delta of some ancient river. On passing from Sheppey 

 tov/ards London, and farther to the west, the vegetable fossils 

 of the London clay disappear, while marine shells are to be 

 found locally, as at Highgate. Many of these shells, though 

 tb.ey belong to extinct animals, resemble those which are 



