2 GEOLOGY, 



is a sub-section of economic geology, relating to the application of 

 geologic facts and principles to mining operations; Atmospheric geology, 

 Glacial geology, and others that define themselves, and are for the 

 greater part but limited aspects of the broad science. 



Dominant processes. — Three sets of processes, now in operation on 

 the surface of the lithosphere, have given rise to most of the details of 

 its configuration, and even many of its larger features. These processes 

 have been designated diastrophism, vulcanism, and gradation. Dias- 

 trophism includes all crustal movements, whether slow or rapid, gentle 

 or violent, slight or extensive. Many parts of the land, especially along 

 coasts, are known to be slowly sinking relative to the sea-level, while 

 other parts are known to be rising. The fact that rocks originally 

 formed beneath the sea now exist at great elevations, and the further 

 fact that areas which were once land are now beneath the sea, are 

 sufficient evidence that similar changes have taken place in the past. 

 Vulcanism includes all processes connected with the extrusion of lava 

 and other volcanic products, and with the rise of lava from lower to 

 higher levels, even if not extruded. Vulcanism and diastrophism may 

 be closely associated, for local movements at least are often associated 

 with volcanic eruptions, and more considerable movements may be 

 connected with the movements of subsurface lavas, even when the 

 connection is not demonstrable. 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 

 protuberances of the lithosphere, while aggradation affects primarily 

 its depressions. 



Astronomic Geology. 



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

 earth is but one of the minor planets attendant upon the sun, and is 

 in no very special way distinguished as a planetary body. Of the eight 

 planets, four, Jupiter, Saturn, Uranus, and Neptune, are much larger 

 than the earth, while three. Mars, Venus, and Mercury, are smaller. 

 Thei^ are a host of asteroids, but all together they do not equal the 

 mass of the smallest planet. The average mass of the eight planets 



