560 STRATIGRAPHICAL GEOLOGY 



and brackish -water shells, while the lower and upper are of fresh- 

 water origin. These beds underlie all the northern part of the Isle 

 of Wight, but except at the western end their outcrop is very 

 narrow. They are well exposed in the cliffs which extend from 

 Headon Hill to Cliff End, and also in Whitecliff Bay at the east end 

 of the island (see map, Fig. 172). In Hampshire they underlie a 

 large part of the New Forest, and the Lower Headon is exposed on 

 the coast in Hordwell Cliff. Eecently they have also been found 

 in Dorset (Isle of Purbeck). 18 



The section at Headon Hill may be regarded as the typical one, 

 although the total thickness is less there than elsewhere, being 

 only 146 feet. The succession at this place is as follows: 19 



Feet 



'Variegated clays with Erodona (Potamomya) gregaria . '21 

 Upper Limestone with Limncea longiscata and Planorbis euom- 

 Headon, - phalus .......... 8 



46 feet Blue clays with the same Limncea and Planorbis . . 5 



Limestone with the same fossils and 2 feet of sand below 12 



M'rlrll fClays with Potamides concavus, Cyrena obovata, etc. . 7 



1 . j e J Limestone with Limncea and Planorbis .... 1 



o^f J 1> 1 Sandy clays with marine fossils ..... 15 



I^Sand and clays with Neritina, Cyrena, and Cerithium . 10 

 'Limestone with Limncea and Planorbis .... 3 



Lower Sands and clays with carbonaceous layers and lignite . 20 

 Headon, Clays and sands with two beds of limestone, Viviparus 

 67 feet angulosus, Nematura parvula, Limncea, and Planorbis . 25 

 Sands and clays with Erodona plana, etc. . . .19 



In Col well Bay the Middle Headon contains many marine shells, 

 such as Ostrea velata, Dosinia (Sinodia) incrassata, Corbula cuspidata, 

 Nucula headonensis. In Whitecliff Bay the marine beds have 

 expanded to 126 feet, and contain many of the Brocklehurst shells 

 mentioned below, while the Lower Headon freshwater beds are 

 reduced to 28 feet, a fact which suggests that part of these lower 

 beds may be replaced by marine deposits. 



The marine beds are found also at Brockenhurst and Lyndhurst 

 in the New Forest, where they yield a rich fauna ; 150 species of 

 shells and corals have been found there, about half of which range 

 up from the Barton Beds, but the fauna as a whole closely resembles 

 that of the Tongrian in Belgium and Germany. Some of the 

 commonest species are Rimella rimosa, Cancellaria muricata, 

 Pisania labiata, Pleurotomaria transversaria, Valuta decora, V. 

 geminata, Cardita deltoidea, Dosinia incrassata, Corbula cuspidata, 

 with Solenastrea cellulosa and many other corals. 



At Hordwell only the Lower Headon is exposed, and the beds 

 are freshwater with a thickness of 83 feet. 20 Many reptilian and 

 mammalian remains have been found at this locality. 



