Chapter 30 



ANIMALS AND PLANTS OF THE PAST 

 AND THEIR RECORDS 



I. RECORDS OF LIFE 



A fossil may be defined as any trace, remains, or impression of a plant 

 or animal of past geologic ages. The science which deals with fossil 

 plants and animals is known as paleontology (Gr. palaios, ancient; onto, 

 being; logos, a study). Paleontology may be divided into two sciences: 

 the one dealing with fossil plants, known as paleobotany (Gr. palaios, 

 ancient; hotane, plant or pasture) and the other dealing with fossil ani- 

 mals, known as paleozoology (Gr. palaios, ancient; zoon, animal; logos, a 

 study). Much of our present knowledge about ancient life has been 

 gained by a very careful and accurate study of the records left by these 

 ancient organisms in the various strata of the earth (Fig. 313). The 

 rocks of the earth's surface are of two kinds according to their origin, sedi- 

 mentary and igneous. The sedimentary rocks, such as limestone, sand- 

 stone, shales, etc., may contain fossils and are formed by the transporta- 

 tion and deposition of small rock particles or by the precipitation of ma- 

 terials from solutions or by the secretions by certain organisms, as in the 

 case of limestones. Igneous rocks (L. igneus, fire), such as volcanic rocks 

 formed by consolidation of molten lava of volcanoes, are produced as the 

 result of heat and do not contain fossils. In the formation of sedimentary 

 rocks the oldest naturally occur at the bottom of a series of strata and the 

 youngest nearest the top. The most ancient fossils thus will be found in 

 the oldest rocks, while the most recent fossils will occur in the youngest 

 rocks. 



II. NATURE AND KINDS OF FOSSILS 



The following are ways in which animals and plants of the past (Figs. 

 313 to 319) have left their records: (1) by actual preservation of the 

 original material of the organism intact, (2) by preservation of the 

 skeletal structures practically unchanged, (3) by natural molds or in- 

 crustations, (4) by petrifaction, (5) by carbonization, and (6) by leav- 

 ing trails and imprints (impressions). 



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