CHAPTER XXI 
THE USES OF FOSSILS! 
Introductory. — Geological study, as carried on now 
for about a century, and extended to all continents, 
has revealed the fact that the earth possesses a varied 
history, one chapter of which is now in progress. This 
history has been one of continual change promoted by 
the agents already discussed. It is the belief of geolo- 
gists that these agents have operated in the past very 
much as they are operating now. There have probably 
been times of more rapid change ; but in a general way, 
1Jn this part of the book the author has departed somewhat from the 
usual custom in books of this kind. Commonly stratigraphic geology is made 
primarily a study of the history of organic life on the globe. In these pages 
the progress of organic life throughout geological ages is stated, but the 
changes in climate and physical geography, particularly of the United States, 
are the main themes. The omission of the more strictly paleontological 
aspect of the subject is not due to any lack of appreciation of its value, but 
rather to the belief that this topic is too important to be treated as would be 
necessary within the limits of an elementary book. A mass of names of 
animals and plants is meaningless to the pupil who has not had more train- 
ing in biology than can be expected of most students in the secondary 
schools. ‘Therefore, the mere catalogue of names is strictly omitted. The 
teacher would do well to have a set of common and typical fossils in the 
laboratory, and to make a study of the fossil fauna of the neighborhood, 
provided the school is situated in a favorable region. 
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