GEOLOGY 



worked out chiefly from the succession of beds of rock formed in the 

 progress of the ages. 



Besides these general subdivisions, there are special applications 

 of geologic knowledge which give rise to other terms. Thus Eco- 

 nomic Geology is concerned with the industrial applications of 

 geologic knowledge, and Mining Geology, which is a sub-section of 

 economic geology, with the application of geologic facts and prin- 

 ciples to mining. Other similar subdivisions might be mentioned. 

 "Ton \ Dominant processes. Three sets of processes, now in operation 

 on the surface of the earth, have given rise to most of its surface 

 features. These processes have been designated Diastrophism, 

 Vulcanism (or Volcanism), and Gradation. Diasjrogto?zLJnlu.des 

 all movements of the outer parts of the lithosphere, whether slow 

 or rapid, gentle or violent, slight or extensive. Many parts of the 

 land, especially along coasts, are known to be sinking slowly relative 

 to the sea-level, while other parts are known to be rising. The 

 fact that sediments originally deposited beneath the sea now exist 

 in some places, at great elevations, together with the fact that cer- 

 tain areas which were once land are now beneath the sea, proves 

 that similar changes have taken place in the past. Earthquakes 

 are another illustration of diastrophism. Vulcanism includes all 

 processes concerned with the movements of lava and other volcanic 

 products, whether extruded at the surface or not. Vulcanism and 

 diastrophism may be closely associated, for local movements are 

 often associated with volcanic eruptions. Gradation includes all 

 those processes which tend to bring the surface of the lithosphere 

 to a common level. Gradational processes belong to two categories 

 - those which level down, degradation, and those which level up, 

 aggradation. The transportation of material from the land, 

 whether by rain, rivers, glaciers, waves, or winds, is degradation, 

 and the deposition of material, whether on the land or in the sea, 

 is aggradation. Degradation affects primarily the higher parts of 

 the lithosphere, while aggradation affects primarily the lower. 



THE EARTH IN THE SOLAI SYSTEM 



The earth as a planet. Though supremely important to us, 

 the earth is but one of the minor planets which revolve about the 



