ELEMENTS OF GEOLOGY 



INTRODUCTION 



The meaning and scope of geology. Geology has to do 

 with the history of the earth and of its inhabitants. Its field 

 is so broad that for the sake of convenience and specialized 

 study it has been divided into numerous branches. Geology 

 is concerned with the different members of the solar system 

 and with other heavenly bodies in so far as they yield evidence 

 as to the origin of the earth, or affect the activities now in 

 progress upon it. This division of the general subject is some- 

 times called Astronomic Geology, and is related closely to the 

 science of Astronomy. The processes and agents at work 

 changing the earth must be studied carefully by the geologist, 

 for they are shaping the present chapter in the history of 

 the earth, and an understanding of them affords also a key 

 by which much of its earlier history, recorded in the rocks, 

 may be read. This phase of the subject is Dynamic Geology, 

 and it has common ground with the special science of Physi- 

 ography or Physical Geography, with Meteorology, the science 

 of the atmosphere, and with other sciences. The study of the 

 remains and impressions of the plants and animals of past 

 ages that are found in the rocks is Paleontology; it is really 

 the historical side of Botany and Zoology. Structural Geol- 

 ogy is concerned with the arrangement of the materials of the 

 earth. That branch of geology which deals with minerals is 

 Mineralogy, that which studies rocks is Petrology; both are 

 connected closely with Chemistry. There are still other 

 divisions of geology, but the ones mentioned are chief, and 

 enough have been enumerated to show that geology is a very 



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