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EVOLUTION AND GENETICS 



Fossils. The fossils which enable us to determine the type of 

 organisms in existence during any of these periods are buried re- 

 mains of organisms or deposits which record in some other sub- 

 stance the original form of the organism. 



In order that fossilization may occur, it is necessary that the 

 organism first be buried in the medium which is to preserve it. An 

 animal may be mired in swampy ground or quicksand, or trapped 

 in asphalt deposits such as those near Los Angeles. In any of 

 these cases, it would be quickly engulfed and protected from dis- 

 integrative forces. Failing such accidents, any body which is 

 preserved must necessarily have been covered quickly enough by 



