EVIDENCES FROM PALAEONTOLOGY 63 
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 1. 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. 
