THE OOLITIC SYSTEM. 



729 



they rest, are marine formations, the limestone, sandstone, and clay of the weald itself are 

 of fresh-water origin. This interesting fact was first established by the indefatigable 

 researches of Dr. Mantell in the district, and is clearly demonstrated by the character of 

 the organic remains. There are no zoophyta, no cephalopoda, but an abundance of fresh- 

 water shells, various land-plants, and relics of terrestrial animals. The palinudas of the 

 Sussex and Purbeck marbles are the shells of river snails. The fact that none of the 

 usual treasures of the deep appear in the wealden, which proclaim the marine origin of 

 the chalk and other formations, but that its fossils belong to the river or to the land, is 

 decisive against its being an oceanic deposit ; and from the appearance presented by its 

 animal arid vegetable remains of having been drifted from a considerable distance, Dr. 

 Mantell arrived at the conclusion, that in this locality some departed Orinoco once rolled 

 its waters, laden with the spoils of the lands it had traversed, like the tropical rivers of 

 the present epoch, and that here its course terminated at the sea in an estuary, at the 

 bottom of which the wealden beds were deposited. This conclusion, the evidence of 

 which has been carefully examined, is universally received^ and it points to the following 

 cycle of change, expressed by Mr. Bakewell : - "The marine beds (upper oolite) on 

 which the Wealden rest, must, at a remote period, have been raised a considerable height 

 above the ocean, and become dry land, having extensive rivers, lakes, or estuaries, filled 

 with fresh-water, in which the Wealden beds were deposited. Again, at a subsequent 

 period, the whole must have sunk deep beneath the surface of the sea, and been covered 

 with a deposition of chalk, a thousand feet or more in thickness. At a more recent 

 epoch, the chalk, with the subjacent beds of Wealden, were raised to their present eleva- 

 tion above the neighbouring sea." 



The vegetable remains found imbedded in this district consist of petrified trunks allied 



to the palms, arborescent ferns, and gigantic reeds of tropical climates. Among the 



animal relics, there are those of birds, turtles, crocodiles resembling the existing gavial, 



rp^s^. the plesiosaurus, pterodactyle, and 



megalosaurus, which have been al- 

 ready noticed, the iguanadon and 

 hylieosaurus, new and gigantic spe 

 cies of the lizard family. 



Iguanadon. This animal, the lar^ 

 gest of the reptiles of a former World, 

 has received its name from its struc- 

 ture approaching to that of the living 

 iguana, especially as it respects the 

 teeth. The existing iguana, of which 

 the cut is a representation of one 

 species, is an inhabitant of Mexico* 



iguana comuta- the Antilles, and South Americaj feed* 



ing on vegetables, living principally in trees, but taking to the water and swimming 

 with facility. A fringe of cartilaginous spines extends along the back from the neck to 

 the tail, and a small conical horn appears on the head. The size of the animal seldom 

 exceeds the length of five feet, and hideous as is its appearance, some of the species 

 are considered very delicate food. The fossil prototype of this reptile resembled it in 

 the construction of the teeth, in possessing a nasal horn, and in being herbivorous; 

 but its dimensions were enormous, realising all that has ever been reported respecting 

 the dragons of fable. The thigh-bone exceeded in bulk that of the largest elephant, and 

 upon good grounds has been estimated at from four to five feet in length. Carefully 

 comparing the bones of the iguanadon with those of the iguana, and taking an average 



