126 EVOLUTION, GENETICS, AND EUGENICS 



were conditions such that these delicate creatures could be preserved. 

 It is not possible to say how far the difficulty caused by the imperfec- 

 tion of the geological record will be removed by the progress of dis- 

 covery. Even as matters stand to-day, the astonishing fact is that 

 so much has been preserved, rather than that the story is so incom- 

 plete. Notwithstanding all the difficulties, the palaeontological 

 method remains one of the most valuable means of testing the theory 

 of evolution, because certain chapters in the history of life have been 

 recorded with a minuteness that is really very surprising." — 

 W. B. Scott, Theory of Evolution. (The Macmillan Company. Re- 

 printed by permission). 



WHAT FOSSILS ARE AND HOW THEY HAVE BEEN PRESERVED 



" Fossils are only animals and plants which have been dead rather 

 longer than those which died yesterday." — T. H. Huxley. 



"Fossils are either actual remains of bones or other parts preserved 

 intact in soil or rocks, or else, and more commonly, parts of animals 

 which have been turned into stone, or of which stony casts have been 

 made. All such remains buried by natural causes are called fossils." — 

 Jordan and Kellogg. 



FOSSILS CLASSIFIED 



Class i. The actual remains of recently extinct animals and 

 plants which have been buried or surrounded by some sort of preserv- 

 ing material constitute the first type under consideration. Such 

 remains have undergone little or no change of the original organic 

 matter into inorganic. Thus we find the complete bodies of great 

 hairy mammoths frozen in the arctic ice. These are so well preserved 

 that dogs have fed upon their flesh. Nearly a thousand species of 

 extinct insects, including many ants, have been obtained practically 

 intact from amber, a form of petrified resin. Innumerable mollusk 

 shells, teeth of sharks, pieces of buried logs, bones of animals buried 

 in asphalt lakes and bogs, have been found in a well-preserved 

 condition. 



Class 2. Petrified fossils. — The process of petrification involves 

 the replacement, particle for particle, of the organic matter of a dead 

 animal or plant by mineral matter. So completely is the finer 

 structure preserved that microscopic sections of preserved tissues, 

 especially of plants, have practically the same appearance as sections 

 made from living organisms. Various mineral materials have been 

 employed in petrification, such as quartz, limestone, or iron pyrites. 



