REVIEWS 



463 



The folded structure of geosynclines is unstable, while the tabular structure 

 of continental areas is stable, and probably always has been so. Such is the law 

 suggested by looking over the surface of the globe. It is therefore proper to divide 

 the subject into several paragraphs corresponding to the five continental areas 

 and the geosynclinal areas whose limits may be taken as known from the work 

 of M. Haug. These are as follows, with the number of quakes in percentages 

 of the total: 



The geosynclines thus include 91 .09 per cent, of the earthquakes that have 

 been reported, as against 8.92 per cent, only for the continental areas, and that, 

 too, in spite of their much larger land surface. 



It may be objected that seismic observations are not old and not sufficiently 

 known, except only for the North Atlantic continent, and that consequently this 

 enormous preponderance of seismicity in favor of the geosynclines is more appar- 

 ent than real, and that it is misleading on account of the lack of information 

 regarding other continental areas. To this it may be replied that the complexity 

 of geographic and geologic conditions of the North Atlantic continent as com- 

 pared with the other four is not inconsistent with the larger number of quakes 

 observed in the former, namely, 5.21 per cent, as against 3.71 per cent, noted 

 for the last four. And even if we do not wish to take this argument into account, 

 it must be admitted that at most the five continental areas cannot furnish more 

 than 25 per cent, of the earthquakes, which would reduce to 75 per cent, in place 

 of 91.08 the seismicity of the geosynclines, as compared with 8.92 per cent, of 

 the continental areas 



It is not expected that the seismic problem will be completely settled by means 

 of this synthetic law. But it is an important result that we can affirm on the 

 strength of statistics the close relation between earthquakes and the zones of the 

 earth's crust where the folds have attained their greatest energy at the same 

 time that the vertical movements have reached their greatest amplitude 



There follows a brief discussion of the several continental and geo- 

 synclinal areas as listed above. The "North Atlantic continent" is 

 defined by him, for purposes of discussion, as comprehending the region 

 lying between the Rocky Mountains and the Urals and north of the Alps 



