1906.] 



SEE— THE CAUSE OF EARTHQUAKES. 357 



layas would doubtless have been broken through by the resulting 

 violence of the volcanic forces. As it was the shallow water, 

 eventually supervening, gave the power for heaving the mountains 

 little by little, and when they attained great height became so feeble 

 or deep-seated that it left them unbroken by volcanic violence. Thus 

 we see why the Alps and the Himalayas, in the main, failed to form 

 volcanoes, and why Africa and Australia are also devoid of these 

 vents (many small ones may have existed and have since lost all 

 trace of this appearance), which chiefly develop near the deep sea, 

 where the sudden exertion of these forces break through the moun- 

 tain tops. This happens in some cases where the mountains are not 

 very high, either because the seat of the explosion is shallow or the 

 fractures such as to offer but little resistance from greater depth. 



In order to break through high mountains, the force has to be 

 extremely powerful, and this is not likely to be the case where the 

 adjacent sea is shallow, as was true south of the Alps and the 

 Himalayas. 



Earthquakes in these regions, however, still continue, and have 

 always been abundant, but they are deep-seated, owing largely to 

 the filling in of the Alpine and Himalayan troughs, and lead to no 

 eruptions, and hence have been called tectonic. They are clearly a 

 survival, due to the same forces which upheaved the mountains, but 

 the sea having so far receded they cannot blow open any cones at 

 this late date. In fact the centers of disturbances usually are some- 

 what remote from the mountains at present and diffused over such 

 an area in the ancient trough that their power for rupture is slight. 



§ 36. Gradual secular desiccation of the oceans indicated by the 

 lozvering of the strand lines throughout the zvorld. 



The raising and lowering of the land by subterranean forces 

 which have effected the withdrawal and encroachment of the sea over 

 the land was first advocated by the Greek geographer Strabo, who 

 adopted the theory of Archimedes that the figure of the ocean sur- 

 face is that of a sphere (cf. Suess, " Face of the Earth," Vol. II, 

 p. 2). This theory has been much developed in modern times and 

 explains numerous movements of the strand line. But according 

 to the elaborate study of this question made by Professor Suess, the 

 elevation and subsidence theory even in the oscillatory form adopted 



