§ 47. THE ANCIENT WORLD. 895 



in the relative number and importance of different orders of 

 animals and vegetables, as are to be found in the vestiges 

 of an earlier world.* 



If we define those areas on a map of the globe, of which 

 the geological structure is known from actual observation, 

 we shall at once perceive how small a proportion of the 

 earth's crust has been examined by the scientific observer ; 

 how large a part of the surface above the water is concealed, 

 by perpetual ice and snow, and is otherwise inaccessible to 

 philosophical research ; and that three-fifths of the entire 

 surface of our planet is buried beneath the waves. These 

 facts are highly suggestive : — they teach us that notwith- 

 standing the immense accumulation of observations made 

 in all parts of the earth, the data hitherto obtained are 

 insufficient to afford a true picture of the full development 

 of organic life, as it existed in the most ancient periods. 



In considering these questions, it must too be remarked, 

 that notwithstanding the differences in the general physiog- 

 nomy of the earliest and latest faunas, there are certain 

 types common to both. Thus, though Orthoceratites, 

 Ammonites, Lituites, &c. represent the cephalopodous mol- 

 lusks in the palaeozoic seas, yet these are associated with 

 true Nautili ; in like manner, with the extinct brachiopoda, 

 the Spirifers, Leptsenae, &c. are found species of the still 

 existing genera of Terebratula, Orthis, and Lingula. So 

 also, in the most ancient tertiary periods, existing species 

 of mammalia, and of terrestrial reptiles, were contemporane- 

 ously inhabitants of the land with the extinct Mastodons and 

 other Pachyderms, and the colossal Tortoises, &c. From these 

 considerations we may infer, that throughout all geological 



* See the ingenious maps of the Geographical Distribution of exist- 

 ing Animals and Plants, in the delightful work of that accomplished 

 authoress, Miss Eosina Zornlin, entitled Researches in Physical Geo- 

 graphy, or the Earth as it is. 



