MOVEMENT IN THE CRUST OF THE EARTH 7 



The land areas have always been subject to degradation by 

 rains, rivers, and waves, and the materials washed from the 

 land have been carried into the sea and there deposited ; thus 

 the continuance of dry land area is comparatively ephemeral. 

 Not only are the lands degraded in this manner, but when they 

 reach the level of the sea they continue to subside ; when above 

 the sea they are speedily unloaded, but when brought to the level 

 of the sea or nearly so the islands, though having their loads dis- 

 charged, continue to sink. The regions which have received the 

 detritus of the islands and are thus loaded by them, are elevated 

 into the island or continental condition ; thus land areas rise to be 

 unloaded and then sink, while oceanic areas are loaded and then 

 rise to become land areas. The extent of this upheaval and 

 subsidence and the vertical movements, involved together with 

 the vast transportation of material from land to sea, seems to be 

 enormous when we contemplate the almost silent and unseen 

 agencies by which it is accomplished. 



In considering large areas of the surface of the earth, as, 

 for example, the great continents or zones of archipelagoes, we 

 reach certain generalizations of prime significance. 



Regions of great denudation are also regions of great depo- 

 sition, regions of great eruption, regions of great upheaval and 

 subsidence, and also regions of great flexure and fracture ; thus 

 denudation and deposition, eruption, displacement, as subsidence 

 and upheaval and as fracture and flexure, are correlated in this 

 manner: that where there is more of one there is more of all; 

 where there is less of one there is less of all. 



Geologists have found no law, condition, or cause by which 

 to explain these phenomena of the earth's crust as the law of 

 gravity explains the constitution of celestial systems. The 

 search for this law has been almost exclusively in one direction, 

 under the hypothesis of a cooling and contracting earth, but 

 with the lapse of time it has been found inadequate. Attempts 

 have been made to compute the amount of contraction supposed 

 to result from the wrinkling of the crust of the earth in anti- 

 clines and synclines. It seems to entirely fail quantitatively. 



