Animals Before Man 



tinuous transcript of past life. Very many 

 animals were by their very structure prevented 

 from leaving any vestige of their former pres- 

 ence, and the vast majority of those that could, 

 perished under such conditions that they failed 

 to do so. The greater part of all fossils are in- 

 accessible, for we can only reach those whose 

 ancient burial-places have been laid bare by 

 the wearing away of overlying rock, or where 

 the edges of strata have been cut through by 

 rivers, or exposed by the mighty thrust of 

 forces that have converted plains into moun- 

 tains. And even after events like these had 

 laid bare the rocky pages wherein the story of 

 the past is written, the hand of Nature, with 

 the selfsame means, has ruthlessly erased all 

 traces of the record before they had been seen 

 by the eye of man. 



There is perhaps no group of animals that 

 illustrates this imperfection of the record so 

 well as birds. There are living to-day not less 

 than 12,000 species, and half of these belong to 

 one group, the Passeres, or perching birds. The 

 ancestors of some of these were living at the 



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