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



spurs being on the side where the slope is gradual, which is always 

 turned toward the sea. Let us now examine the meaning of this 

 arrangement. In the new work on Geology by Chamberlin and 

 Salisbury (Vol. I, p. 542-3) we read: 



"Mountain-forming Movements. — Along certain tracts, usually near the 

 borders of the continents, and at certain times, usually separated by long 

 intervals, the crust was folded into gigantic wrinkles, land these constitute 

 the chief type of mountains, though not the only type. The characteristic 

 force in this folding was lateral thrust. The strata were' not only arched, 

 but often closely folded, and sometimes intensely crumpled. In extreme 

 cases, like the Alps, the folds flared out above, giving overturn dips and 

 reverse strata, as illustrated in the chapter on " Structural Geology," pp. 

 501-51 1. In these cases there was an upward a-s well as a horizontal move- 

 ment, for the folds themselves were lifted; but the more horizontal thrust 

 so much preponderated, and was so much the more remarkable, that the 

 upward movement was overshadowed. It is well to note, however, that 

 these mountain ranges are crumpled outward and not inward, as might 

 be expected if they resulted simply from the shrinkage of the under side 

 of a thin shell. The folds are sometimes nearly upright and symmetrical, 

 and sometimes inclined and asymmetrical, as illustrated in the chapter referred 

 to. Where the folds lean, the inference has been drawn that the active 

 thrust came from the side of the gentler slope, the folds being pushed over 

 toward the resisting side, and this seems to be commonly true." 



Thus we have good authority for the statement that the lateral 

 thrust came from the side of the gentler slope. It is well known 

 that the gentler slope is turned towards the sea, and thus we realize 

 that the forces which pushed the mountains horizontally was directed 

 from the*adjacent ocean. 



In his great work on " Face of the Earth," ^ Professor Suess 

 records the following facts, all bearing on the above view : 



1. In Vol. I, p. 452, Suess shows that the tangential movement 

 in the Himalayas and Burmese Mountains on the opposite sides of 

 the Bramaputra are in opposite directions, each being directed from 

 the center of the river — exactly what the present theory requires, 

 and not explainable on any other hypothesis. 



2. In Vol. II, p. 34, Suess shows that the mountain folds in the 

 eastern part of the United States " have been produced by a tan- 

 gential movement directed from the existing Atlantic Ocean toward 

 the mainland." On page 139 he shows that the same principle holds 

 for South America.. 



^ Oxford Translation by Dr. Hertha Sollas. 



