PROCEEDINGS OE GEOLOGICAL SOCIETIES. 



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the mineral character is the same throughout, it follows that there must 

 have been a slow subsidence going on, to make up for the shallowing of the 

 sea by the continuous deposition of sediment, and thus to allow the life of 

 the age to keep the same during the whole time of deposition of these hun- 

 dreds of feet of clay, which it could not do if the depth of the sea were so 

 much lessened as would be the case without subsidence. 



The only place where any number of fossils have been found in the Lou- 

 don Clay in Kent, is the Isle of Sheppey, where, however, the cliffs have 

 yielded a rich harvest both of species and specimens. These, which are 

 from the higher part of the formation, give evidence of the existence in 

 those long-past ages of corals, star-fishes, sea-urchins, an abundance of 

 Crustacea (crabs, lobsters), often forming the nucleus of septaria, mollusks 

 in great plenty, fish (especially sharks, the teeth of which are very common), 

 and rays and reptiles (turtles, tortoises, crocodile, and serpent.) The re- 

 mains of a small pachydermatous mammal have been found near Heme Bay. 

 The most remarkable of the Sheppey fossils, and which are far less common 

 elsewhere, are the plant-remains. These are chiefly of the leguminous 

 and coniferous orders and palms, and consist of fruits, seeds, and stems. 

 They are in iron-pyrites (sulphide of iron), and therefore very difficult to 

 keep, as that substance often decomposes when exposed. They show that 

 the neighbouring land on which they grew must have been much warmer 

 than our present temperate climate ; and this evidence is strengthened by 

 that of the remains of the Moliusca, amongst which the univalve Nautili, 

 Cones, Cowries, and Volutes show that the sea in which they lived must 

 have been in a warm climate. Shells of many other genera occur, such as 

 Fusus, Natica, Pleurotoma, Hostellaria, and the bivalves Cardium, Pec- 

 tunculus, and Teredo, a great deal of the wood having been bored by the 

 last. These shells, like the vegetable remains, are in the state of casts in 

 iron-pyrites. 



The middle and lower beds of the London Clay, near TVhitstable and 

 Heme Bay, have yielded fewer fossils. 



A noteworthy feature of the London Clay cliffs is the frequent occur- 

 rence of landslips ; nearly the whole face of the sloping cliff being generally 

 made up of the fallen masses. In dry summer-time the clay is shrunk by 

 the heat, and deep cracks are formed ; when rain falls, much water finds 

 its way down these cracks, loosens the clay, and makes it slippery, so that 

 masses can more readily fall down. The destructive action of the weather 

 is, however, greatest in the winter, when the water in the deep cracks 

 freezes, and the vast force put forth in its expansion, on becoming ice, 

 loosens the beds, which would then tend to slip down after a thaw. Early 

 in the present year (1883) a slip occurred which threw a long strip of land, 

 about two acres in extent, some way down the cliff : the young wheat was 

 growing very well in its strange position. 



5. The Lower Bag shot Sand occurs in the form of a thin outlier on the 

 highest part of the Isle of Sheppey ; the only place in Kent where the 

 London Clay is capped by this formation, which has been worn off alto- 

 gether in other parts of the county. The sand is light- coloured, more 

 clayey towards the bottom, and generally passes into the sandy clay form- 

 ing the uppermost part of the London Clay. It may be seen for more than 

 a mile along the cliff near Minster, and is at the most some 30 feet thick. 



Although of so small extent and thickness, this outlying mass of sand is 

 of much geological value. Firstly, it proves that the Bagshot series once 

 spread over these parts, as the outliers at Hayleigh and elsewhere on the 

 opposite side of the Thames prove its former extension over Essex ; and, 

 secondly, it enables us to calculate the thickness of the London Clay from 



