46 



THE YOUNG NATURALIST. 



Nucula similis 



„ oligyratus 



Ostrea Vectensis 



„ platystoma 



Paludina globuloides 



„ rotundatus 



„ lenta ■ 



„ Sowerbii 



„ orbicularis 



Pupa oryza 



Panopsea minor 



„ perdentata 



Planorbis discus 



Succinea Edwardsi 



„ obtusus 





Headon Series. 



These beds are about 170 feet thick, they are divided into the Upper — 

 fresh-water and brackish beds ; Middle — intermarine ; and Lower — fresh aud 

 brackish water beds. 



The Upper Headon Beds. 



These form the greater part of what is usually termed the " Upper Fresh- 

 water Formation." The strongest masses of the freshwater limestone in 

 Headon Hill belong to this section, but are only represented in Whitecliff 

 Bay by a few thin and inconspicuous sandy concretionary bands. These beds 

 consist in their highest part of brackish water bands, abounding in Polamo- 

 mya, and a large variety of Cyrena obovata. The shells of the freshwater 

 limestones are the same as those of the Lower Headon beds, with the ex- 

 ception, perhaps, of a large Paludina and so-called Bulimus polilus. 



The Middle Headon Beds. 



These consist of what are usually called the " Upper Marine Formation." 

 At Headon Hill, however, this division mainly indicates brackish water con- 

 ditions. At Colwell, the same bed assumes a marine character, and presents 

 large bands of oysters, with many other marine shells, and at Whitecliff is 

 still more strongly marked, and the thickness of purely marine deposits much 

 greater than westwards. 



The Lower Headon Beds. 



These consist of fresh and brackish-water beds, abounding in fossils, which 

 for the most part, are identical with those of the upper division. At Headon 

 Hill, and Colwell Bay, there are thick limestone bands in this part of the 

 series, while at Whitecliff Bay all the beds are clays and marls. The lower 

 bed of this series rest upon sands, equivalents of the Upper Bagshot beds, 

 but are unfossiliferous in this locality. 



