THE INFLUENCE OF GEOLOGY ON HORTICULTURE. 



407 



hood of Royston, plums are grown to high perfection. Again, in the 

 neighbourhood of Worthing, in Sussex, over the chalk very large quan- 

 tities of hot-house grapes are grown as well as hardy fruits, and there is 

 a very old fig orchard, said to have belonged to Thomas a Becket, proving 

 the mildness of the climate. On the chalk cliffs between Dover and Deal 

 the wild cabbage, ancestor of the cultivated forms, grows freely, and 

 rhubarb, which contains much oxalate of lime in its stem, thrives 

 particularly well over chalk, if well manured. With the chalk ends the 

 secondary period of the rocks. 



The Tertiary Period comprises rocks in which are found fossil remains 

 of plants and animals similar to, or identical with, those now existing. 



L_L'~* [Fig. 76. — Map showing Principal Fruit-growing Districts of Kent. 



The first group of beds is the'Eocene, which includes the Thanet sands, 

 the London and plastic clays, and other beds. 



The Thanet Sands, so named by Sir Joseph Prestwich, are specially 

 well seen at Pegwell Bay and at Reculvers, and occur in patches 

 overlying the chalk in the north-east of Kent. The fruit lands around 

 Dartford, Bexley, St. Paul's Cray, St. Mary Cray, Hockenham, Swanley, 

 Well Hill, Swanscombe, Betsham, Southfleet, Cobham, Shorne, and 

 Gillingham (near Chatham) rest chiefly on these sands. This rock is 

 a fine grey or buff-coloured sand. It makes a free soil, which can be 

 worked in almost all weathers, moderately fertile, but if well manured 

 very productive, and much of the best fruit and market garden land lies 

 over it, growing all kinds of hardy fruit and vegetables well, but the 



