4 To the River Plate and Back 



lived in the seas; such as corals, shell-fish, trilobites, 

 and in the upper strata curious fishes, mostly long since 

 extinct. In the Mesozoic beds, which are of marine 



GEOLOGIC 

 AGES 



QUATERNARY 

 (AGE OF MAN] 



CENOZOIC 



OR 



TERTIARY 



AGE OF MAMMALS) 



MESOZOIC 



(AGE OF REPTILES) 



PALEOZOIC 

 (AGE OF FISHES; 



ARCHEAN 



OR 



EOZOIC 



IGNEKXJS 



OR 



AZOIC 



Fig. i. Diagram showing the succession of the geologic ages 

 and the origin in time of animals and plants. (Modified after 

 Leconte.) 



origin, we find the remains of marine life, but we also 

 find in some of the strata great beds of coal, formed no 

 doubt on swampy land raised above the level of the 

 sea; and we find further fishes and reptiles in great 

 numbers, curious birds with teeth, and in the upper 



