22 Dr. Wright on the Geology of the Isle of Wight. 



very fossillferous, and contain immense numbers of Potamides 

 ventricosus and Cyrena obovata. 



The shelly blocks on the shore containing these elegant shells 

 are derived from the debris of these beds. 



No. 16. "The Neritina bed." The origin of tbis bed on the 

 sbore is concealed by debris ; it is seen however at low-water 

 mark below Bramble Chine when a ground sea has cleared away 

 the sand. 



This bed is seen well in situ beneath tbe flagstaff at Cliff Cot- 

 tage reposing upon the fossiliferous bands of No. 15, It inclines 

 at an angle of about 2°. Here it is a rich fossiliferous seam about 

 18 inches in thickness, divisible into three sbelly zones. The 

 inferior zone contains Potamides margaritaceus, P. cinctus, Me- 

 lania muricata, Melanopsis minuta, M. fusiformis, and myriads of 

 Nematura of a new species. 



The middle zone contains Neritina concava in great abundance, 

 and in a high state of preservation, with all their delicate- 

 coloured pencillings, like recent shells : along with these which 

 characterize the bed, are, Potamides margaritaceus, P. cinctus; 

 Nematura ; Melanopsis fusiformis, Serpula tenuis, Cijrena cycladi- 

 formis ; vegetable impressions and seeds of Chara medicaginula, 

 and C. tuber culata [Gijrogonites) . 



The upper zone contains Natica depressa, Mytilus affinis, Os- 

 trea, new species, and a profusion of Cyrena obovata. 



The Neritina bed at Headon Hill is charged with lignite, black 

 clay and vegetable remains, but I collected its characteristic 

 fossils at the western escarpment. 



No. 17. Blue sandy clay measm-ing from 4 to 9 feet ? in thick- 

 ness in different parts of its course, and containing fossiliferous 

 seams in its upper and lower laminae ? 



The upper shelly band contains Cyrena obovata and Potamides 

 margaritaceus. In the lower layers, hymncea longiscata was ob- 

 served to occur in a crushed state sparingly. 



No. 18. Lymnsean limestone (No. 2) forms a conspicuous bed 

 in this section. It rises on the shore about 390 feet north of 

 Colwell Chine, and inclines at an angle of about 3°. It runs out 

 on the cliff near the flagstaff of the Coast-guard station beyond 

 Warden Point. It has been denuded from the cliff in the centre 

 of Tollands Bay. It appears in situ at the north side of Headon, 

 and with the underlying clays and sands forms the promi- 

 nent mural band which runs nearly horizontal through the 

 northern slope of that hill. At its southern escarpment, where 

 it overlooks Alum Bay, it forms a well-defined bed. Its inclina- 

 tion here increases, and it is suddenly curved up together with 

 the under- and the overlying beds to an angle of 20°, and soon 

 after abruptly ceases. 



