INTßODUCTION 



DEFINITION AND SCOPE OF PALEONTOLOGY 



Paleontology (Aoyos row TraXatCov ovTOiv) is the Science which treats of 

 the life which has existed on the globe during former geological periods. It 

 deals with all questions concerning the structure, Classification, relationships, 

 descent, conditions of existence, and distribution in time and space of the 

 ancient inhabitants of the earth, as well as with those theories of organic and 

 cosmogonic evolution which result from such inquiries. 



Under the term of fossils are understood 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. The criterion which 

 determines the fossil character of organic remains is the geological age of the 

 formation in which they occur, whereas their mode and State of preservation, 

 or the fact of their belonging to extinct or to still living species, are merely 

 incidental considerations. Although fossils have, as a rule, undergone more 

 or less radical changes during the process of fossilisation, and are usually 

 transformed into mineral substances, nevertheless, under exceptionally 

 favourable conditions (as in frozen ground, amber, resin, peat, etc.), plants 

 and animals may be preserved through geological periods in a practically 

 unaltered state. Carcasses of mammoths and rhinoceroses entombed in the 

 frozen mud-cliffs of Siberia, and inclusions of insects, spiders and plants in 

 amber are none the less genuine fossils, in spite of their having sustained no 

 trace whatever of mineral infiltration. 



A considerable number of plants and animals occurring as fossils in Tertiary 

 and Pleistocene formations belong to still living species ; while, on the other 

 hand, the remains of forms which have become extinct during historical times 

 (Ehijtina, Alca, Didus, Pezophaps, etc.) can no more be classed as fossils in the 

 true sense of the word than all such recent organisms as may chance to 

 become buried in deposits now forming under the present prevailing orographic 

 and climatal conditions. 



The changes which organic bodies undergo during the process of fossilisa- 

 tion are partly chemical and partly mechanical in their nature.^ According 

 as certain portions of the original substance are removed, or are replaced atom 



^ White, Charles J., Conditions of preservation of invertebrate fossils. Bull. U.S. Geol. and 

 Geog. Survey Territ., 1880, vol. v. , p. 133. Trahucco, G., La Petrificazione. Pavia, 1887. 

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