The Eocene Formation of Headon and Alum Bay. 7 



unsolved problem. Calcareous, argillaceous, and siliceous matter, 

 the whole or part of which was in a state of solution, seem origi- 

 nally to have formed the mass of this formation. The tranquil state 

 of the ocean at this period may be inferred from the perfect preser- 

 vation of numerous minute and delicate fossils. This was suc- 

 ceeded by an era of turbulence, during which, however, the depo- 

 sition of the Plastic sands and clays mark periods of rejiose. When 

 all seems to have become calm, the London clay was deposited. 



And here we are struck with the analogy which exists between 

 the vegetable and animal remains of this stratum with those of 

 the tropics at the present day. 



The extraordinary event of the elevation and subsidence of 

 the chalk in the Isle of Wight and Dorset must have taken place, 

 as we have seen, after the deposition of the London clay. A 

 change like this, unexampled in historic times, it would of course 

 be impossible to account for. All we can do is to point out some 

 of the characteristics which are still traceable. As was pointed 

 out above, the Dorset and Isle of Wight chalk formations seem to 

 have been originally united so that at the period when the depo- 

 sitions were formed, there was one vast bay open towards 

 the east, extending from Beachy Head north westward to Ports- 

 mouth and Southampton, thence, including the New Forest, south 

 westerly to Dorchester, where it curved shortly rouud past 

 Lulworth and Studland to the Needles. 



This vast bay of the sea seems to have been the estuary of 

 some mighty river, which washed down in its course forests of 

 lofty fig-trees, palms, and oaks, besides vast quantities of alluvial 

 matter. The result was that a bar was formed across the 

 mouth of the river. What had formerly been an arm of the sea 

 became a fresh-water lagoon teeming with the animal life of the 

 period ; and the vast river must have emptied itself by some fresh 

 outlet into the sea. 



Some time after this some mighty commotion seems to have 

 arisen in the ocean, and either the sand-bar across the estuary 

 to the eastward gave way before it, or perhaps the mass of waters 

 from the Atlantic pouring on broke down the western limit of the 

 chalk, and once more covered the river's estuary with its waters. 

 And such a catastrophe has not been unparalleled in historic 

 times. As late as the year I272, the waters of the Atlantic, which 

 had been, as it were, pent up northward by an unceasing succes- 

 sion of south-westerly gales, were by a sudden change of the 

 wind, hurled full force on the coast of Holland. The dyke at the 

 Ilondsbosche gave way, and in one night smiling villages and 

 plains were buried beneath the ocean, iind (34,000 men swept from 

 off the face of the land. 



