CHAPTER VIII 

 EVIDENCES OF EVOLUTION (Continued) 



2. THE GEOLOGICAL RECORD 



If the changes which have occurred in organisms during past 

 ages were recorded completely, the record would show us exactly 

 how one species has given rise to others, and how the gradual 

 change from group to grouj) through increasing degrees of com- 

 plexity has been accomplished. The result would be a phylo- 

 genetic tree rooted in the beginning of life, every l)ranch complete 

 in its connection with the whole. In the chronology of the various 

 steps would be evidence of the infinite slowness of phylogenetic 

 change, and in the characteristics of the organisms would be re- 

 flected the conditions of environment under which they lived. 



Fortunately some twigs from this tree are preserved, and 

 through the study of these fragments of the record and the many 

 evidences of physical change in the earth's surface, the sciences of 

 geology and paleontology give us a satisfactory, if incomplete, 

 account of past evolution. In the findings of geologists there are 

 evidences of great transformations of the earth, of the elevation 

 of land masses and mountain ranges, the inundation of great areas 

 by the oceans, frigid climates resulting from extension of polar 

 ice caps and tropical conditions following their recession. The 

 evidences of these changes involve almost incomprehensible 

 movements of material which could not have been brought about 

 in less than millions of years. Paleontology correlates witli these 

 facts the records of organic remains, and in the whole we find frag- 

 mentary evidence of phylogenetic change which is a valuable 

 corollary to that shown in existing organisms. 



Rock Formation. From evidence which we need not consider 

 here, geologists have concluded that the earth was once in a molten 

 state. The first rocks which appeared in the crust as it cooled 

 were therefore igneous. By weathering and erosion of these pri- 

 mordial rocks soils were formed and sediments of various kinds 

 were carried down to the oceans. Here they settled in layers of 

 mud and sand. Minute organisms living in the sea also settled to 



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