MODERN STUDIES OF EARTHQUAKES. 369 



Japan between 1885 and 1892; Julius Schmidt, former director of 

 the observatory in Athens, enumerated three hundred severe and 

 dangerous and fifty thousand light shocks for Phocis alone between 

 1870 and 1873, of which not a trace of land changes or depressions 

 can be perceived, aside from superficial avalanches (on Parnassus, for 

 example) and subsidence of meadows and other spongy soil, like the 

 famous depression of the Molo at Lisbon. 



All this speaks so emphatically against the tectonic origin of earth- 

 quakes that it can not be considered as a general cause. Even the 

 mighty disturbances and shocks of the times when such ranges as the 

 Alps and Himalayas were lifted up can prove nothing for the present 

 time; for the conditions, the mechanical work and acting forces, of 

 the earth were quite different, and the latter much greater and more 

 acute than in our time, as the number and magnitude of the volcanoes 

 of those ages show, before which ours are almost as nothing. We 

 have no adequate comprehension of the way that mechanical work 

 was done. A depression like that of the plain of the Rhine could 

 certainly not have taken place without severe earthquakes ; but we do 

 not know how they may have come to pass, for we have nothing 

 analogous to them. The upper strata of the earth's crust are broken 

 up, fissured, and cavernous; hence purely local minor earthquakes 

 may undoubtedly be produced by cavings-in, landslides, and set- 

 tlings of small extent. But this explanation, in view of the nature 

 of the crust, is not possible for strong earthquakes, even in the upper 

 layers, which send their waves far over the land ; their origin must be, 

 almost of necessity, in the greater deeps beneath the crust, far down 

 where the immense gas globe of the interior is constantly forcing 

 its way into the fluid band, and this into the solid stone; in those 

 zones of changing conditions a mighty movement must be inces- 

 santly prevailing. The pressure upon the gases of the interior dimin- 

 ishes here, and the excessive temperature as well. This can not take 

 place without changes. Temperature and pressure now fall, now 

 rise again, but continue very high through it all. The dissociated 

 gases unite and separate again, and most violent explosions are infal- 

 libly produced thereby. Water exists in the interior in immense 

 masses, and that not solely in consequence of percolation from the 

 surface. Vapor at very high pressure separates into its elements — ■ 

 hydrogen and oxygen — the reunion of which ensues with violent 

 explosions, similar to our gas explosions, which must be very numer- 

 ous in the interior of the earth, and accompanied with great develop- 

 ment of force. The principal effect of such explosions is, of course, 

 against the cooler and more weakly resisting sides, and therefore 

 not toward the interior but toward the crust and the weakest parts 

 of it, toward the rupture lines of the zones of disturbance, the syn- 



TOL. LIV. — 27 ♦ 



