INTRODUCTION 



DEFINITION AND SCOPE OF PALAEONTOLOGY 



Palaeontology (Aoyos ruv TraAcuwv e'l/Twv) 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 properties, classification, relationships, 

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

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

 cosmogonic evolution which result from such inquiries. 



By fossils, or petrifactions, 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 evidence which is in 

 all cases conclusive as to 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, as a rule, fossils have 

 undergone more or less radical changes during the process of fossilisation, and 

 are usually converted into mineral substances, as the term petrifaction indi- 

 cates, 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 by no means inconsiderable number of plants and animals occurring 

 strictly fossil 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 (Bhytina, 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. 1 According 



1 M7///C, Charles A., Conditions of preservation of invertebrate fossils. Bull. U.S. Geol. and 

 Geog. Survey Territ., 1880, vol. V. p. 133. 



Tmbucco, Oiac., La Petriflcazione. Pavia, 1887. 



VOL. I B 



