416 CONSISTENCY OP GEOLOGY WITH SACRED HISTORY. 



the number and magnitude of the petrified trees which remain. It is 

 equally evident, that it was submerged before the Purbeck and Weal- 

 den strata began to be deposited ; for the dirt-bed, and its contents, 

 are covered by the freshwater limestone of the former. The tropical 

 forest of Portland must, therefore, have gradually and tranquilly sub- 

 sided (like many subterranean forests of the modern epoch) beneath a 

 body of fresh water, sufficiently profound to admit of the accumulation 

 of the limestone and fluviatile strata that compose the Wealden. 

 What contemporaneous changes took place in other parts of Europe, 

 it would be foreign to our purpose, and perhaps, in the present state 

 of our knowledge, in vain to enquire ; but we may remark, that the 

 submergence of so extensive a tract of country, probably produced in 

 other regions important mutations in the relative level of the land and 

 water. At this epoch, then, the land and its tropical forest sank to 

 the depth of many hundred feet, and became the bed of a vast lake or 

 estuary, into which we have the clearest evidence that a river flowed, 

 and formed a delta, made up of the debris of the rocks which compo- 

 sed its bed, intermixed with the remains of the animals and vegeta- 

 bles of the country from whence its waters were derived ; for, as Mr. t 

 Bakewell has sagaciously remarked, a river that could form a delta of 

 such extent as the Wealden, it must have required the drainage of a 

 vast continent to supply.* 



The proofs of the Wealden having been the delta of some ancient 

 river, are so fully stated in the preceding chapter, that it is unneces- 

 sary to dwell upon the subject. Of its original extent, our conjec- 

 tures must necessarily be extremely vague : Dr. Fitton has, however, 

 ingeniously instituted a comparison between the known superficial 

 surface of the Wealden, and the deltas of some modern rivers. As- 

 suming that the occurrence of the Wealden strata at Beauvais is es- 

 tabhshed, this eminent geologist computes that the remains of the delta 

 of the Iguanodon period, are from west to east, or from Lulworth 

 Cove, to the boundaries of the Lower Boulonnois, about 200 miles ; 

 and from north-west to south-east, or from Whitchurch to Beauvais, 

 220 miles ; the total depth or thickness being about 2000 feet.f This 

 but little exceeds the modern deltas of the Ganges, and the Mississip- 

 pi ; and is not equal to that of the Quorra, or Niger, which forms a 

 surface of 25,000 square miles, being equal in extent to one half of 

 England. 



We have no data from which to calculate the probable duration of 

 the Iguanodon epoch ; it is, however, manifest that no brief period 

 could have sufficed for that profuse evolution of animal life, of which 

 we have such positive evidence in the organic remains. It may here, 

 too, be remarked, that the vegetables and animals of this era, like the 

 forest of Portland, denote a tropical climate, and belong to species and ' 



* Had the fossil vegetables of the Wealden been identical with those of the Isle 

 of Portland, it might have been supposed that the latter was dry land at the Iguan- 

 odon period: but although the vegetable remains in both deposits indicate the 

 floras of tropical clirhates, they are totally distinct from each other, and belong to 

 different species and genera. 



t Geology of Hastings, p. 58. 



