CHAPTER XXVI 



PALEONTOLOGY 



JUST as we attempt to read and interpret the history of man's 

 progress in the handicrafts, through the remnants of tools and 

 pottery which are found in various parts of the world, so we attempt 

 to read and interpret the changing conditions which have taken place 

 in the earth's crust by the study of geological and paleontological find- 

 ings. Geology concerns itself with the changes in the earth itself, while 

 paleontology seeks to build up a meaningful account of the changes 

 which may have taken place in living organisms throughout the past, 

 as demonstrated by their fossil remains (Fig. 245). 



There are two general ways in which layers of rock and soil have 

 been laid down. The first has come about by the formation within the 

 earth of great masses of molten substance which was then thrown out 

 by volcanic action. Such masses harden to form minerals and other 

 heat products. If the minerals then become concentrated, they are called 

 ores. All such products formed by heat are known as igneous forma- 

 tions. 



The second way in which changes have come about is this : Various 

 horizontal soil-layers have been shifted about by climatic changes such 

 as a subsiding of land surfaces and an elevation of the edges of the 

 ocean. This causes the lowered continent to be covered by shallow 

 water, and later, when this condition is again reversed, a layer of sedi- 

 ment is left behind. It is in this sediment that millions of marine-forms 

 of life are stranded. If the sediment hardens, and these marine organ- 

 isms are safely protected from air and superficial decay, their bodies 

 will be preserved as fossil remains. 



Fossil remains are, therefore, observed most frequently in the 

 deposits on the floors of lakes, in peat-marshes, in the deltas of river- 

 mouths, and under the stalagmites in caverns in limestone districts. 



The exceptional conditions necessary to preserve organic forms will 

 rarely be found everywhere, so that we must remember that no matter 

 how many fossil remains may be found, only a very infinitesimal portion 

 of the living forms of any given period will become known to us. Then, 

 too, in those which are preserved, most, if not all, of the softer parts of 

 the organism are destroyed, only the hard portions remaining. 



The necessity for coordinating the facts found in many and varying 

 ways is of prime importance in the science of paleontology, for without 

 such coordination there is neither sense nor value in its study. This 

 will be demonstrated quite clearly in what follows. 



