488 



THE WONDERS OF GEOLOGY. Lect. V. 



" If it be asked where the continent was placed from whose ruins 

 the Wealden strata were derived, and by the drainage of which a great 

 river was fed, we are half tempted to speculate on the former existence 

 of the Atlantis of Plato ; for the story of the submergence of an ancient 

 continent, however fabulous in history, may be true as a geological 

 event. Its disappearance may have been gradual ; and we need not 

 suppose that the rate of subsidence was hastened at the period Avhen 

 the displacement of a great body of fresh water by the cretaceous sea 

 took place. Suppose the mean height of land drained by the river 

 of the Wealden estuary to have been no more than 800 or 1000 feet : 

 in that case, all except the tops of the mountains would be covered as 

 soon as the fundamental oolite, and the dirt-bed were sunk down 

 about 1000 feet below the level which they occupied when the forest 

 of Portland was growing. Towards the close of the period of this 

 subsidence, both the sea would encroach, and the river diminish in 

 volume, more rapidly ; yet in such a manner, that we may easily 

 conceive the sediment at first washed into the advancing sea, to have 

 resembled that previously- deposited by the river in the estuary. 

 In fact, the upper beds of the Wealden, and the inferior strata of 

 the Greensand, are not only conformable, but of similar mineral 

 composition. 



" It is also a remarkable fact, that the same Iguanodon Mantelli, 

 which is so conspicuous a fossil in the Wealden, has been discovered 

 in the overlying Kentish-rag, near Maidstone. Hence we may infer, 

 that some of the Saurians which inhabited the country of the great 

 river, continued to live when part of the country had become sub- 

 merged beneath the sea. Thus in our own times, we may suppose 

 the bones of alligators to be frequently entombed in recent fresh-water 

 strata in the delta of the Ganges ; but if part of that delta should sink 

 down so as to be covered by the sea, marine formations might begin 

 to accumulate in the same space where fresh- water beds had previously 

 been formed ; and yet the Ganges might still pour down its turbid 

 waters in the same direction, and transport the carcasses of the same 

 species of alligator to the sea ; in which case their bones might be 

 included in marine as well as in subjacent fresh-water strata." 



4. LlTHOLOGICAL STRUCTURE OF TIlE IGUANODOM 



coujntry. — The nature of the rocks and strata of which 

 the country of the Iguanodon was composed is also a sub- 

 ject of considerable interest; and from the first moment that 

 the fluviatile origin of the Wealden suggested itself to my 



