GEOLOGY 



CHAPTER I. 

 PRELIMINARY OUTLINE. 



Geology treats of the structure of the earth, of the various stages 

 through which it has passed, and of the hving beings that have dwelt 

 upon it, together with the agencies and processes involved in the changes 

 it has undergone. Geology is essentially a history of the earth and its 

 inhabitants. It is one of the broadest of the sciences, and brings under 

 consideration certain phases of nearly all the other sciences, particularly 

 those of astronomy, physics, chemistry, zoology, and botany. It also 

 embraces the earlier expressions of mental development and of life- 

 relationships, chiefly as found in the lower animals. 



Subdivisions. — Naturally so broad a science has many special 

 aspects which constitute subdivisions, in a sense, though they are 

 rather dominant phases than independent sections. That phase which 

 treats of the outer relations of the earth is Cosmic or Astronomic geology; 

 that which treats of the constituent parts of the earth and its material 

 is Geognosy, of which the most important branch is Petrology, the science 

 of rocks. That branch which investigates the structural arrangement 

 of the material, or 'Hhe architecture of the earth,'' is Geotecfonic, or 

 Structural geology; while that which deals with the surface changes 

 and topographic forms, that is, with the face of the earth, is Physio- 

 graphic geology. The study of the fossils that have been preserved in 

 the rocks, and of the faunas and floras that these imply, constitutes 

 Paleontologic geology, or Paleontology. The treatment of the succession 

 of events forms Historical geology. This is chiefly worked out by the 

 succession of beds laid down in the progress of the ages, which con- 

 stitutes Stratigraphic geology. The treatment of causes, agencies, and 

 processes is the function of Dynamic or Philosophic geology. 



Besides these there are special applications which give occasion 

 for other terms, as Economic geology, which is concerned with the 

 industrial applications of geologic knowledge; Mining geology, which 



