The Eocene Formation of Headon and Alum Bay. 5 



At the bottom of these beds, and between them and tlie thick 

 black clay immediately over the glass sands, there is found a layer 

 two inches or more in thickness, of a dark brown coaly matter, 

 resembling that found in the bottom of peat bogs, and it seems to 

 be a similar substance which tinges these beds. 



At Headon, as far as I can discover, no marine fossils are 

 found iu these beds, though in the memoirs of the Geological 

 Survey, fish-bones and other marine remains are mentioned as 

 being found in the same beds at East Cowes. But the whole of 

 the Northern coast of the isle of Wight has been for ages in a 

 state of constant ruin owing to the action of the sea and to 

 landslips, so that fresh water and marine shells are found together 

 in confusion on the shore as at Cowes. Occasional alternations 

 between marine and freshwater shells might be expected, on the 

 supposition that they denoted a gradual change taking place in an 

 arm of the sea before it became a freshwater lake, or else they 

 might be attributed to the occasional irruptions of the ocean at a 

 subsequent period. 



It is in this formation in the Paris basin that the beds of 

 gypsum are found. These are sometimes deposited on the marine 

 shelly calcareous sand, in which case they contain marine shells. 

 In these also are beds of white marl, containing Lymneus Planorbis 

 and other freshwater shells, constituting the lowest freshwater for- 

 mations, which according to Cuvier and Brogniart, appear to have 

 been formed during the change of the Paris basin from the state 

 of a marine bay to that of a freshwater lake. Two more beds of 

 gypsum are found in this formation, in the upper of which the 

 bones of unknown quadrupeds and birds are found : over this 

 again are thick beds of argillaceous and calcareous marls contain- 

 ing silicated palm trunks. 



The total absence of gypsum and quadruped remains in the 

 Isle of Wight beds, points to the fact that though probably of 

 contemporaneous origin, these beds must have been formed under 

 very different circumstances. 



III. Over the lower freshwater formation in the Isle of Wight is 

 found a stratum of clay and marl containing vast numbers of shells, 

 whoU}' marine and in very good preservation ; they difl'er 

 remarkabl}' from those of the lower marine, and some of them 

 bear a remarkable resemblance to recent shells. 



The substance of the bed is chiefly of a light green marl, and 

 separated from the freshwater formation by a bed of sand only a 

 few inches in thickness. 



About the centre of this formation occurs a vast scam of 

 Cylherea iticrassata, commonly known as the Venus Bed ; and at 

 Col well Bay, at a fissure called Brambles Chine, there is a large 



