AND THEIE EXTENSION IN HEETFOHDSHIEE. 165 



have been named the Oldhaven Beds, though at Oldhaven Gap 

 the beds of this horizon are rather clayey than stony. Bounding 

 the south side of the Thames Valley extends a series of flat-topped 

 hills, with deeply-cut indentations which being usually richly 

 wooded add greatly to the beauty of the district. The high-level 

 flats are formed of the Oldhaven pebble-beds, and the pretty dells 

 are due to the erosion of the easily disintegrated beds by the water 

 which is stopped in its downward course by the argillaceous beds 

 below, and which has found an outlet at various points along the 

 escarpment. 



Nowhere perhaps are these remarkable beds of pebbles better 

 seen than at Blackheath, one of the plateaux formed by them. The 

 pebbles are found to be completely rounded or oval, without the 

 admixtirre of any angular or even subangular ones. Moreover they 

 are all of one material. They are all flint pebbles of a blue-black 

 colour. We have no difficulty in concluding, therefore, that the 

 Oldhaven pebble-bods are derived from the waste of a Chalk 

 district, and the belief is entertained that they have formed origin- 

 ally a great sliingle bank well out at sea, and were not shingle 

 beaches at the foot of a chalk cliff, for in that case subangular flints 

 would have been plentifully intermingled with those which had 

 been longer exposed to the rollijig action of the sea waves, and 

 which consequently wore more completely rounded. 



The London Clay. — To give anything like a description of the 

 succeeding formation, the great argillaceous deposit known as the 

 London Clay, with its interesting fauna and flora, much more time 

 than is at our disposal this evening would be required. So much 

 was, however, said on this member of the Eocenes by Professor 

 Morris in his learned lecture last year to the members of this 

 Society, and printed in the 'Transactions,' that it will be un- 

 necessary for me to do more than remind you of the salient facts 

 recorded by investigators of the London Clay. In the London 

 Tertiary Basin the London Clay occupies a very extensive area, 

 stretching from near Hungerford in the west to the coast of 

 Essex in the east, and forming the greater part of the counties 

 of Middlesex and Essex, while in the Hampshire Basin the London 

 Clay is seen resting against the Plastic Clay of the Isle of "Wight. 

 At some depth below the surface this deposit is a blue clay of 

 unifoinn consistency ; but where exposure has taken place the 

 colour is broAvn, consequent upon the more complete oxidation 

 of the iron contained in the clay, and crystals of selenite are 

 abundant, while the clay itself is less compact and uniform in 

 character. 



The fauna as well as the flora of the London Clay indicate 

 warmer conditions than prevailed during the Thanet Sands or tho 

 subsequent Woolwich Series period, and indeed to some geologists 

 give conclusive evidence of a warm or even a hot climate. Certain 

 it is that the inhabitants of tropical seas at the present time, such 

 as turtles, nautili, volutes, and the plants growing on the banks 

 of tropical rivers, such as palms, had representatives in the London 



