828 THE POPULAR SCIENCE MONTHLY. 



manifestations of gigantic force thus plainly registered are the effects 

 of ancient back-foldings and of lateral or horizontal pressures. It is 

 as if the crust of the earth had become too large for the supporting 

 nucleus, and had, to keep in contact with it, to shrink up and bend 

 upon itself. These foldings and fractures have given origin to chains 

 of mountains. 



Now, the geological study of earthquakes has shown that their cen- 

 ters of impulsion are in relation with the ground-lines of fracture and 

 dislocation. The disturbed bands are usually longitudinally parallel 

 to the chains. A recent example of this linear disposition has been 

 added in the latest earthquake in Andalusia, the major axis of which, 

 according to M. Fouque, is parallel to the mountain-crests of the prov- 

 ince, as well as to the numerous faults that cut it up. Another im- 

 portant point to be noticed is that the countries in which the mount- 

 ains have most recently acquired their latest relief are the ones in 

 which these subterranean agitations are particularly frequent. 



The Andalusian masses which have been so rudely disturbed within 

 a fewmonths partake of all the structural conditions that have just 

 been noticed. The Sierra Nevada is among the youngest chains of 

 mountains on the globe. The tertiary strata around it have been pow- 

 erfully lifted up, sometimes to more than three thousand feet above 

 the sea, without having their horizontality destroyed. According to 

 M. de Botella there are also, in different places at the foot of the chain, 

 strata regarded as quaternary that have been tilted into an inclination 

 of 65. Furthermore, numerous faults furrow the country, while the 

 parts that have been most disturbed, according to Macpherson, are 

 upon the faults that terminate the crystalline mass of the Sierra Tejea 

 and Almijara. The numerous thermal springs of the region are fur- 

 ther evidences of the deep fractures that traverse it. 



Similar conditions, dislocations, and recent age, are found in other 

 regions subject to subterranean perturbations. They appear notably in 

 that part of the Mediterranean basin which we have spoken of as espe- 

 cially agitated, although it is distant from volcanoes ; in the Apennines, 

 the Lebanon, and the mountainous masses of Dalmatia and Croatia bor- 

 dering on the Adriatic. The configuration of the northern coasts of 

 that sea, so exceptionally slashed and cut by deep indentations, results 

 from the complexity of the fractures that have determined the outlines 

 of their principal features. Even the chain of the Alps, where shocks 

 are felt nearly every year, acquired its final relief only at a compara- 

 tively recent epoch. It is conceivable under such conditions that the 

 interior masses are not yet at equilibrium nor wholly subsided, and 

 that they contain vacant spaces affording room for further sinkings. 



According to what seems to be the dominant opinion of the day, 

 there are two kinds of earthquakes : those which are due to volcanic 

 actions, and of which the vapor of water is the prime mover ; and those 

 which are the effect of such ruptures of the equilibrium of the solid 



