742 GEOLOGY. 



in the sea, when the teredince lived upon it, perforating it in all directions. But before 

 they settled on the wood the branch of a tree must have been floated down to the sea by 

 a river, uprooted perhaps by a flood, or torn off and cast into the waves by the winds ; 

 and thus our thoughts are carried back to a period when the tree grew for years on dry 

 land, enjoying a fit soil arid climate." The Isle of Sheppey, at the mouth of the Thames, 

 is an outlier of the London clay, being composed of it, and one of the most interesting of 

 geological sites, on account of the abundance and nature of its fossils. Besides the usual 

 shells, there are here to be found the remains of vertebrated fishes ; of crustaceans ; of 

 birds, serpents, and turtles ; of plants allied to the cucumber, bean, cypress, and laburnum ; 

 of the fruits of palms, and specimens resembling the spices of the East. So numerous are 

 the vegetable relics, that they have been estimated as indicating many hundreds of species, 

 mostly of a tropical nature. The imagination may be pardoned, arising from the occur- 

 rence of these vegetable forms, that when they were imbedded in their present site the 

 elevated parts of England formed a number of spice islands like the Moluccas, enjoying 

 an equatorial warmth, whose products, committed by natural agencies to the waves, were 

 drifted hither by an oceanic current, and laid up in their present resting-place. A more 

 sober conclusion is, that the climate of our northern zone still possessed a tropical tem- 

 perature, and that here was the estuary of a river which brought down these specimens of 

 the flora of the neighbouring land. The third and uppermost group of the London basin 

 consists of arenaceous deposits, the sands of Highgate, Hampstead, Finchley, and Bagshot 

 Heaths, with very few organic remains, forming the wastes abandoned to their native 

 furze, which mark the neighbourhood of the capital. 



The Hampshire basin includes an area of the mainland out of that county, east and 

 west, and the northern part of the Isle of Wight, which is, in fact, a disrupted mass from 



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Alum Bay, Isle of Wight. 



the south coast of England. Strata here alternate of marine and fresh-water origin, and 

 so far this tertiary district of the eocene era differs from that just noticed. This fact 

 indicates alternations in the level of the land with reference to the sea ; and the existence 

 of an estuary into which a river poured its waters during the elevation of the land, 

 bearing along specimens of the organisms of an interior country, which were deposited in 

 its bed, the whole being subsequently submerged and re-elevated. The fresh-water strata 

 contain very perfect remains of tortoises and crocodiles, with the bones of mammalia, 

 belonging to land animals identical with those which we shall have to notice as occurring 

 in the Paris basin, a formation of the same epoch. By far the most remarkable locality 

 in this district is Alum Bay, whose vertical and variously-coloured strata at once arrest 

 the eye of the spectator, the tints of the cliffs being so bright and varied that they have 



