508 



THE THEORY OF EVOLUTION 



ground water after the mud has changed to rock. In this manner 

 a mold of the shell may be formed, but shell-bearing animals 

 usually leave only their shells and vertebrates usually no remains 

 but bones and teeth. The soft parts of animals are never preserved 

 in the rocks, although they may leave imprints as fine as a human 



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■ Fig. 270.— Tracks of dinosaurs (cf. Fig. 269). 



Above, where a dinosaur sat down; below, photograph of a slab of Connecticut V.alley 

 brownstonc from specimen in museum of Amherst College. (From Lucas, "Animals of 

 the Past," courtesy, .\merican Museum of Natural History.) 



finger print (cf. Fig. 266 A). Even an animal hke a jellyfish may 

 leave an impress upon a mud flat and be preserved if soon covered 

 with fine sediment, as has happened in at least one instance. In a 

 similar manner, the tracks of small animals that have walked or 

 crawled upon muddy beaches have become part of the fossil 

 record; and the tracks of large animals, such as the great reptiles 

 known as dinosaurs, may be found in places where no traces of 

 their bones remain (Fig. 270). Leaves buried in mud have formed 



