184! Mr Mantell on the Geological Age of Reptiles. 



tinct from those of the present period, a great proportion being 

 referrible to the Gavials ; that division which has long slender 

 snouts. 



In the fresh-water formations that intervene between the 

 ooHte and the chalk, namely, the Purbeck, Hastings' sands and 

 clays, and the Tilgate grit, the remains of several of the genera 

 of the reptiles we have before noticed, occur ; but those which 

 are strictly marine, such as the Ichthyosaurus, are either alto- 

 gether wanting, or of very rare occurrence. At the period of 

 the formation of these deposites, turtles, both marine and fresh- 

 water, existed in great numbers, having for contemporaries the 

 Megalosaurus, one or more species of Plesiosaurus, several 

 species of Gavials and Crocodiles, and probably Pterodac- 

 tyles. At this epoch we have also an enormous herbivorous 

 reptile, essentially differing from any of the oviparous quad- 

 rupeds now existing, and surpassing in magnitude even the 

 Megalosaurus. This is the Ignanodon (so named from its 

 teeth resembling those of the recent Iguana). A thigh-bone 

 of this creature, twenty-three inches in circumference, has been 

 discovered in the grit of Tilgate forest ; the teeth are as 

 large as the incisors of the rhinoceros, and the vertebrae, 

 claw-bones, and other parts of the skeleton, bear the same 

 relative proportions. This creature, like some of the recent 

 species of Iguanas, had warts or horns on its snout, and an 

 appendage of this kind has been found of the size and shape 

 of the lesser horn of the rhinoceros ! From the prevailing cha- 

 racter of the form of the bones, it is probable that this animal 

 was shorter in proportion to its bulk than the recent lizards, to 

 which it is more nearly allied ; and marvellous as it may appear, 

 we cannot but infer that some individuals attained a height of 

 nme or ten feet, and were from sixty to a hundred feet in length! 

 A circumstance even more extraordinary than its magnitude, 

 IS that of its having performed mastication like the herbivorous 

 mammalia, its teeth, which are of a very peculiar form, being 

 in general worn down by the operation of grinding its food. 



The vegetables associated with the remains of the Iguanodon 

 are all of a tropical character, and consist of various kinds of 

 ferns,[|and of large plants allied to the dragon-blood plant. The 

 strata in which they ai-e found, unlike those of the oolite which 

 preceded, and of the chalk which followed these deposites, have 



