CHAPTER IV 

 THE LOWER GREENSAND 



FOR ages the Wealden river flowed, and over its vast delta 

 laid down its depth of river mud. The land was gradually 

 sinking ; for continually strata of river mud were laid 

 down over the same area, all shallow-water strata, yet 

 counting hundreds of feet in thickness in all. At last a 

 change came. The land sank more rapidly, and in over 

 the delta the sea water flowed. The sign of coming change 

 is seen in the limestone band made up of small oysters 

 near the top of the Wealden strata. Marine life was 

 beginning to appear. 



Above the Wealden shales in Sandown Bay may be 

 seen a band of brown rock. It is in places much covered by 

 slip, but big blocks lie about the shore, and it runs out to 

 sea as a reef before we come to the Red Cliff. The blocks 

 are seen to consist of a hard grey stone, but the weathered 

 surfaces are soft and brown. They are full of fossils, all 

 marine, sea shells and corals. The sea has washed in 

 well over our Wealden delta, and with this bed the next 

 formation, the Lower Greensand, begins. The bed is 

 called the Perna bed, from a large bivalve shell (Perna 

 mulleti) frequently to be found in it, though it is difficult 

 to obtain perfect specimens showing the long hinge of 

 the valve, which is a marked feature of the shell. Among 

 other shells are a large round bivalve Corbis (Sphcera) 

 corrugata, a flatter bivalve Astarte, and a smaller oblong 

 shell Panopaa, also a peculiar shell of triangular form, 

 Trigonia, one species T. caudata has raised ribs running 

 across it, another T. dadalea has bands of raised spots. 



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