THE LONDON CLAY— ITS FOSSILS— ITS HISTORY. 37 



is 140 feet thick ; at Camden Town Station (L. & N. W. R.), 

 144 feet; at the Zoological Gardens, Regent's Park, 155 feet; 

 at Cricklewood, 2 1 2 feet ; and at the old well at the bottom of 

 the Lower Heath, 289 feet. 



At Hampstead Heath, at Harrow, and at High Beach in 

 Essex, remnants of the Bagshot Sands form the summit of the 

 land, and hence at these points the full thickness of the London 

 Clay in those districts remains. At the Crystal Palace, Sydenham, 

 the whole of the once overlying Bagshot Sands has been taken 

 off, but a portion of the uppermost bed of the London Clay, the 

 Upper Sandy London Clay, caps the hill, so that had Sydenham 

 Hill not been worn down quite so much it would have had at the 

 summit a patch of Bagshot Sands like Hampstead Hill. 



Since the London Clay forms a member of the Tertiaries 

 of the Hampstead Basin, it may be safely concluded that it has at 

 one time extended over the Chalk area lying between the two 

 Tertiary Basins. There has* therefore been a continuous bed of 

 the London Clay from Harwich to the Isle of Wight, where 

 portions may be seen in White Cliff and Alum Bays. But that 

 was not its extreme extent by any means, for it is represented on 

 the other side of the Channel, in France, near Dieppe, and also in 

 the neighbourhood of Dunkirk, while some beds in the Belgian 

 area appear to be of the same age, and were doubtless deposited 

 in the same sea. 



What changes in the geography of this part of the European 

 area are told to us by this superficial glance at the extension of 

 the London Clay ! for it tells of continuous continental land with- 

 out the English Channel, without the straits of Dover, without 

 the white cliffs of Albion, and without the Solent and Spithead to 

 insulate the Isle of Wight. But it tells much more than this and 

 of an earlier epoch. It tells of the time when the whole of the 

 area it now occupies was sea, and from its utmost extension 



