THE CRUST OF THE EARTH. 



tribes of the lower animals, by insects, fishes of the genus Lapidotus, 

 and, among the colossal class of reptiles, by the Hylseosaiirus, and 

 among terrestrial quadrupeds, by the Iguanodon. 



66. Among the numerous animals characteristic of the Cretaceous 

 period may be mentioned the Mososaurus of Hoffman, the Belem- 

 nites mucronatus, the Terebratula plicatilis. 



67. In cases where a group of strata is characterised by the pre- 

 valence of a particular family of fossils, which first appear at its 



Fig. 8. Ammonites Humpriasiamus. 



lowest, and finally disappear at its uppermost layer, the succeeding 

 strata are often distinguishable one from another, by the preva- 

 lence in them of a different species of this generic family. Thus 



Fig. 11. 



Nautilus Dauians. 



for example, the Ammonites, so called from their spiral form, re- 

 sembling the horn sculptured on the head of Jupiter Ammon, 

 commence in the Silurian and finally disappear after the chalk. 

 But each stratum, from that in which the family first appears 



