PART 11. CHAPTER XVL 



203 



Wealden Group Fossil Plants. 



water in tropical regions. Of Saurian lizards there are at least 

 five genera ; the Crocodilej Plesiosaur, Megalosaur, Iguanodon, 

 and Hylseosaur. The Iguanodon, of which the remains were 

 first discovered by Mr. Mantell, was an herbivorous reptile, and 

 was regarded by Cuvier as more extraordinary than any with 

 which he was acquainted ; for the teeth, though bearing a great 

 analogy to the modern Iguanas which now frequent the tropical 

 woods of America and the West Indies, exhibit many striking 

 and important differences (see Fig. 190.). It appears that they 

 have been worn by mastication ; whereas the existing herbivo- 

 rous reptiles clip and gnaw off the vegetable productions on 



which they feed, but do not chew 

 them. Their teeth, when worn, 

 present an appearance of having 

 been chipped off, and never, like the 

 fossil teeth of the Iguanodon, have a 

 flat ground surface, (see Fig. 189.), 

 resembling the grinders of herbivo- 

 rous mammalia. From the large 

 bones, found in great numbers near 

 these teeth, and fairly presumed to 

 belong to the same animal, it is 

 computed that the entire length of 

 this reptile could not have been less 

 than seventy feet. 



The bones of birds of the order 

 Grallce or Waders have been discovered by Mr. Mantell in the 

 Wealden, and appear to be the oldest well authenticated exam- 

 ples of fossils of this class hitherto found in Great Britain.* But 

 no portion of the skeleton of a mammiferous quadruped has yet 

 been met with. 



The vegetable remains, which are numerous, exhibit many 

 characters of a tropical flora, some being allied to the living 

 genera Cycas and Zamia, (see Fig. 194.,) others to large Equi- 

 seta. There are also Coniferse allied to Araucaria, and other 

 genera of warm climates, (see Fig. 191.) besides numerous 

 ferns. (See Fig. 192.) 



Passage of Wealden beneath Chalk. — It has been already 

 seen that the chalk and green-sand have an aggregate thickness 

 of 1000 or sometimes 1500 feet. It is therefore a wonderful 

 fact that after penetrating these rocks, we come down upon a 

 subjacent freshwater formation from 800 to 1000 feet in thick- 

 ness. The order of superposition is clear, for we see the weald 



* Mantell. Proceedings Geol. Soc. vol. ii. p. 203. 



Teeth of Iguanodon. 



Fig. 190. 



Crown of tooth in Pointed tooth of 

 adult, icorn down, a young animal. 

 Mantell. Mantell. 



