424 



ANIMAL STUDIES 



sea or might be preserved in the mud of small ponds. 

 That is, instead of finding in the stratified rocks of any 

 portion of the earth remains of all the animals which have 

 lived on that portion since the earth began, we shall find, at 

 best, only remains of a few kinds of those animals which 

 have lived on this portion of the earth when it was covered 

 by the ocean or by a great lake. 



339. Geological epochs and their animals. Thus, the 

 great body of fossil remains of animals reveal only a broken 

 and incomplete history of the animal life of the past. But 



the record, so far as it 

 goes, is an absolutely 

 truthful one, and when 

 the many deposits of fossils in all parts 

 of the different continents are examined 

 and compared, it is possible to state nu- 

 merous general truths in regard to past 

 life and the succession of animals in time. 

 The science of extinct life is known as 

 paleontology. 



The study of Paleontology has revealed 

 much of the history of the earth and its 

 inhabitants from the first rise of the land 

 from the sea till the present era. This 

 whole stretch of time how long nobody 

 knows is divided into eras or ages ; these 

 ages usually into lesser divisions called periods, and the 

 periods into shorter lengths of time called epochs. Each 

 epoch is more or less sharply distinguished from every 

 other by the different species of animals and plants which 

 lived while its rocks were being deposited. In the earth's 

 crust, where it has not been distorted by foldings and 

 breaks, the oldest stratified rocks lie at the bottom of the 

 series, and the newest at the top. The fossils found in 

 the lowest or oldest rocks represent, therefore, the oldest 

 or earliest animals, those in the upper or newest rocks 



FIG. 245. A Pterodac- 

 tyl or flying reptile 

 (Rhamphorhynchus 

 gemmingi), Jurassic 

 of Bavaria. After 

 ZITTEL. 



