CHAPTER XXX. 



FOSSILS, THEIR CHARACTER AND MODE OF PRESERVATION. 



Definition and Limitation of the Term Fossil. 



Fossils are the remains of animals and plants, or the direct evi- 

 dence of their former existence, which have been preserved in 

 the rocks of the earth's crust. By direct evidence is meant the im- 

 pressions left by animals in transition, the structures built by them, 

 etc. Beds of iron ore and deposits of apatite or of crystalline 

 limestone must be considered indirect and not always reliable evi- 

 dence of the former existence of organisms, since, in these cases, 

 organisms were only the agents active in their formation. Under 

 remains preserved in the earth's crust must be included those 

 formed in the northern ice fields, for we have seen that these ice 

 masses are to be regarded as a portion of the rocky crust of the 

 earth, though in most respects the least permanent one. 



It has been a common custom to limit the term fossil to those 

 remains which were buried prior to the present geologic period. 

 This will be seen from the common text-book definitions of this 

 term. A few of them may be quoted. Fossils: "All remains or 

 traces of plants and animals which have lived before the beginning 

 of the present geological period, and have become preserved in 

 the rocks." (Zittel, Eastman's translation.) "Remains of animals 

 and plants which have existed on the earth in epochs anterior to 

 the present, and which are buried in the crust of the earth, are 

 called fossils." (Bernard's Elements, adapted from the English 

 translation.) "All the natural objects which come to be studied 

 by the palaeontologists are termed 'fossils' . . . Remains of 

 organisms . . . found ... in those portions of the earth's 

 crust which we can show by other evidence to have been formed 

 prior to the establishment of the existing terrestrial order . . ." 

 (Nicholson and Lydekker, Manual of Pala^ntology.) "Of those 

 animals and plants which have inhabited the earth in former times, 

 certain parts, decomposable with difficulty, or not at all, have been 



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