How the Hixtonj of the Pant fs 



that they crumbled to pieces and disappeared. 

 There is another class of fossils in a measure 

 intermediate between the actual preservation 

 of a bone or shell and its mere impression ; and 

 this is where such objects as the shell of a crab 

 or the leaf of a tree have been pressed extreme- 

 ly thin, but have left their exact outline in color 

 on the rock, as if painted by the hand of na- 

 ture. This color-printing is usually due to the 

 presence of iron in the soil in which the object 

 was buried, and its combination with organic 

 matter makes a stain. 



But if flesh and animals of soft texture per- 

 ish completely so far as actual substance is con- 

 cerned, the impressions such objects made in 

 the sand or mud on which they rested, and the 

 casts formed by the mud which settled about 

 or in them may remain ; and it is wonderful to 

 find that such delicate creatures as soft-bodied 

 jellyfish, or sea-nettles, have left traces of their 

 former presence even in some of the most 

 ancient rocks. This, of course, could happen 

 only where the water was quiet and soft mud 

 plentiful, so that these delicate animals were 



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