340 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



In the greater periodic movements, probably all the basins participated more 

 or less, but some seem to have been more active than others. For example, 

 in the last great mountain-making period, the Pacific basin seems to have 

 been more active than the Atlantic, while in the similar great event at the 

 close of the Paleozoic, the opposite seems to have been true. The squeezing 

 up of the continents doubtless took place simultaneously with the settling of 

 the basins. The true conception is perhaps that the ocean-basins and con- 

 tinental platforms are but the surface forms of great segments of the litho- 

 sphere, all of which crowd towards the center, the stronger and heavier seg- 

 ments taking precedence and squeezing the weaker and lighter ones between 

 them. The area of the more depressed or master segments is almost exactly 

 twice that of the protruding or squeezed ones. This estimate includes in the 

 latter about 10,000,000 square miles now covered with shallow water. The 

 volume of the hydrosphere is a little too great for the true basins, and it 

 runs over, covering the borders of the continents. The amount of the over- 

 flow fluctuates from time to time, and may be neglected in a study of the 

 movements and deformation of the lithosphere." 



^^ Among the major group of squeezed segments we find: (i) 

 Eurasia, (2) Africa, (3) North America, (4) South America; and 

 the minor group includes Australia, Antarctica, the East Indian 

 platform, and Greenland. The depressed or master segments are the 

 oceans: (i) The Pacific, (2) the Indian, (3) the North Atlantic, 

 (4) the South Atlantic ; and a minor group of smaller seas, as the 

 Arctic, the Mediterranean, the Caribbean, and the chain of deep 

 pits between the Philippines and the platform of Borneo. 



The authors discuss the crowding of these segments towards the 

 center and the crumpling which follows along their edges, accom- 

 panied by fracture and slipping. 



" If these segments be regarded as the great integers of body-movement, 

 two-thirds of them taking precedence in sinking and the other third in suffer- 

 ing distortion, it is easy to pass to the conception of subsegments, moving 

 somewhat differently from the main segments, so as to aid in their adjust- 

 ment to one another, and thus to the conception of plateaus and deeps. It 

 is easy also to pass to the conception of mutual crowding and crumpling at the 

 edges of these segments, accompanied by fracture and slipping. These con- 

 ceptions perhaps represent the true relations between the massive move- 

 ments of the abysmal and continental segments, as well as the less massive 

 plateau-forming movements and the mountain-forming distortions. The 

 mountains and plateaus are probably the incidental results of the great 

 abysmal and continental readjustments. 



" The great movements are probably to be attributed to stresses that 

 gradually accumulated until they overcame the rigidity of the thick massive 

 segments involved, and forced a readjustment. In accumulating these 

 stresses, some local yielding on weak lines and at special points was an 



