352 GEOLOGY 



the slow wrinkling of mountain folds. Rivers may wear down 

 their channels across a mountain range as fast as it rises athwart 

 them, and the movements of continents are even slower; but far 

 apart as these contrasted movements are, they are doubtless asso- 

 ciated in cause; and the earthquake shock is often merely an inci- 

 dent in the formation of a mountain range or in the movement of 

 a continent. 



The great movements may be classed (1) as continent-making 

 (2) plateau-forming and (3) mountain-folding; or as (1) general 

 (epeirogenic) or (2) as concentrated (orogenic); as (1) vertical and 

 (2) horizontal, and dynamically, as (1) thrust and (2) stretching 

 movements. These distinctions are analytical conveniences but 

 are not exclusive of one another, for continental movements often 

 involve mountain-making, vertical movements usually involve 

 horizontal movements, and stretching usually attends the outer 

 bends of thrust folds. 



Present movements. Observations on seacoasts show that 

 some shores are slowly rising and some slowly sinking, relative to 

 the ocean-level. It is not certain what these movements are relative 

 to the center of the earth. All parts of the coast may be sinking, 

 some faster than others, while the ocean-surface goes down at an 

 intermediate rate; or, theoretically, all parts may be rising, but 

 at different rates. Some lands may be actually rising relative 

 to the center of the earth, and others sinking, while the ocean-level 

 has an intermediate movement or none at all. We are accustomed 

 to take the sea-level as a standard, as though it were stationary, 

 which is probably not the fact. A general shrinkage of the earth 

 is probably going on, carrying down the surface of both land and 

 sea. It is possible that the shrinkage is so great that upward 

 warpings and foldings do not usually equal it, and hence nearly all 

 movement may be really toward the earth's center. This seems 

 to be implied by the crumpling of the surface. The popular dispo- 

 sition is to regard earth movements generally as " upheavals." 

 There is also a predilection for regarding the rigid land as moving, 

 and the mobile sea-level as fixed. In reality, the sea is an ex- 

 tremely adaptive body which settles freely into the irregular 

 hollows of the lithosphere and is shifted with every warping of the 



