I'GNEOFS BOCKS. Those rocks are 

 termed igneous which are con- 

 sidered to have once been in a 

 fluid state from the action of heat 

 upon them, and in that state to 

 have overflowed, to have been in- 

 jected among, or to have been pro- 

 pelled through, other rocks. 



IGUA'NA. A species of lizard, a native 

 of many parts of America and the 

 "West Indies, rarely met with any 

 where north or south of the tropics. 

 It is from three to five feet long, 

 from the end of the snout to the 

 tip of the tail. It inhabits rocky 

 and woody places, and feeds on 

 insects and vegetables. Cuvier 

 states that the iguana subsists upon 

 fruit, grain, and leaves : Eosc, that 

 it lives principally upon insects. 

 It nestles in hollow rocks and trees. 

 The female lays its eggs, which 

 have a thin skin like those of the 

 turtle, and are about the size of 

 those of a pigeon, in the sand. 

 Though not amphibious, they are 

 said to be able to remain under 

 water an hour. When they swim, 

 they do not use their feet, but place 

 them close to their body, and guide 

 themselves with their tails. Capt. 

 Belcher found, in the Island of 

 Isabella, swarms of iguanas, that 

 appeared omnivorous. This state- 

 ment proves both Cuvier and Bosc 

 to be correct. The .teeth of the 

 iguana are not fitted for comminu- 

 ting its food, and it is said to 

 swallow it whole. 



IGTTA'NODON. An extinct fossil colossal 

 lizard, discovered in the strata of 

 Tilgate Forest by that indefatigable 

 historian of the chalk and Wealden 

 formation, the late Dr. Mantell. 

 He observes, " the discovery of the 

 teeth and other remains of a non- 

 descript herbivorous reptile in the 

 strata of Tilgate Forest, a reptile 

 pronounced by Cuvier to be 'encore 

 plus extraordinaire quo tous ceux 

 dont nous avons connoissance,' is 

 one of the most gratifying results 



[ 230 ] I G U 



of my labours." The remains of 

 one of these immense animals have 

 lately been found in the Kentish 

 rag, near Maidstone. The Kentish 

 rag is a grey arenaceous limestone, 

 belonging to the Shanklin sands. 

 From the great resemblance in the 

 dentature, as well as in many other 

 extraordinary characteristics, of this 

 immense reptile to that of the igu- 

 ana, Dr. Mantell determined Jon 

 naming it the Iguanodon, signify- 

 ing an animal having teeth like 

 the iguana. In the perfect teeth, 

 and in those which have been but 

 little worn, the crown is somewhat 

 of a prismatic form; widest, and 

 most depressed, in front; convex 

 posteriorly, and rather flattened at 

 the sides. As soon as the tooth 

 emerges from the gum it gradually 

 enlarges, and its edges approach 

 each other and terminate in a 

 point, making the upper part of the 

 crown angular ; the edges forming 

 the side of this angle are deeply 

 serrated, or dentated ; and the 

 teeth exhibit two kinds of pro- 

 visions to maintain sharp edges 

 along the cutting surface : the first 

 the serrated edge already described; 

 the second, a provision of compen- 

 sation for the gradual destruction 

 of this edge, by substituting a plate 

 of thin enamel, to maintain a cut- 

 ting power in the anterior portion 

 of the tooth, until its entire sub- 

 stance was consumed. These teeth 

 were sometimes two inches and a 

 half in length. While the crown 

 of the tooth was diminishing above, 

 an absorption of the fang was 

 proceeding below, caused by the 

 pressure of a new tooth rising to 

 replace the old one, until by con- 

 tinual consumption, both above and 

 below, the middle portion of the 

 older tooth was reduced to a hollow 

 stump, which fell from the jaw to 

 make room for its more efficient 

 successor. The size attained by 

 the iguanodon appears to have been 



