EARTH FEATUEES AND THEIR MEANING 



CHAPTER I 

 THE COMPILATION OF EARTH HISTORY 



The sources of the history. The science which deals with the 

 chapters of earth history that antedate the earliest human writ- 

 ings is geology. The pages of the record are the layers of rock 

 which make up the outer shell of our world. Here as in old 

 manuscripts pages are sometimes found to be missing, and on 

 others the writing is largely effaced so as to be indistinct or even 

 illegible. An intelligent interpretation of this record requires a 

 knowledge of the materials and the structure of the earth, as 

 well as a proper conception of the agencies which have caused 

 change and so developed the history. These agencies in opera- 

 tion are physical and chemical processes, and so the sciences of 

 physics and chemistry are fundamental in any extended study of 

 geology. Not only is geology, so to speak, founded upon chemis- 

 try and physics, but its field overlaps that of many other im- 

 portant sciences. The earliest earth history has to do with the 

 form, size, and physical condition of a minor planet in the solar 

 system. The earliest portion of the story belongs therefore to 

 astronomy, and no sharp line can be drawn to separate this chap- 

 ter from those later ones which are more clearly within the domain 

 of geology. 



Subdivisions of geology. The terms " cosmic geology" and 

 "astronomic geology" have sometimes been used to cover the 

 astronomy of the earth planet. The later earth history develops, 

 among other things, the varied forms of animal and vegetable life 

 which have had a definite order of appearance. Their study is 

 to a large extent zoology and botany, though here considered 

 from an essentially different viewpoint. This subdivision of our 

 science is called paleontological geology or paleontology, which 



B 1 



