DIVISIONS OF GEOLOGY 7 



of the earth, to the contemplation of infinities of energy, space, 

 and time, bringing him at last face to face with the mystery 

 of the Universe. To this inscrutable mystery every line of scien- 

 tific inquiry must ultimately lead, for human knowledge is like 

 a dim taper which illumines a little space, but is surrounded by 

 immeasurable darkness. 



The very diverse lines of inquiry which together make up the 

 science of geology, must be classified and divided for the purposes 

 of orderly treatment. The following are the principal divisions of 

 the science. 



i. Dynamical Geology, or the study of the forces which are 

 now at work in modifying the surface of the earth, and of the 

 chemical and mechanical changes which they effect. This is the 

 key by which we may interpret past changes. 



2. Structural Geology, or the study of the materials of which 

 the earth is composed and of the manner in which they are 

 arranged ; together with such explanations of the modes in which 

 the arrangement was produced, as may be inferred from the 

 structure. 



3. Physiographical Geology is an examination of the topo- 

 graphical features of the earth and of the mode in which they 

 were produced. Primarily, this subject is a province of physical 

 geography, but it is a valuable adjunct to geology. 



The three foregoing divisions together constitute a larger division, 

 which is called Physical Geology, and which is contrasted with — 



4. Historical Geology. — * This is the study of the earth's history 

 and development, the changes of level between land and sea, of 

 topography, of climate, and of the successive groups of animals 

 and plants which have lived upon the globe. As we have seen, 

 the historical is the dominant standpoint in geology, the main 

 problem of which is to interpret the records of the earth's history. 

 The other departments are to be regarded as the means to this 

 great end. 



