SCIENCE. 



FRIDAY, MARCH 6, 1885. 



COMMENT AND CRITICISM. 

 The increased favor with which the oro- 

 genic theory of earthquakes — the theory that 

 regards earthquakes as the effect of disturb- 

 ances due to mountain growth — has been 

 looked upon in recent years must be accounted 

 a distinct gain for physical geology. The vol- 

 canic theory, now rationally limited, has long 

 been more popular. It is not long since 

 Mallet, who has been widely quoted as an 

 authority on the question, committed himself 

 to the narrow statement that "an earthquake 

 in a non-volcanic region may, in fact, be 

 viewed as an uncompleted effort to establish a 

 volcano," although he afterwards held a broader 

 opinion. Lyell wrote in the last edition of his 

 'Principles' (1876), very much as in his first 

 (1830), that "the principal causes of the vol- 

 cano and the earthquake are to a great extent 

 the same, and connected with the development 

 of heat and chemical action at various depths in 

 the interior of the globe." More lately, Dau- 

 bree maintains a similar view, even after refer- 

 ring to the suggestions of Dana, Suess, and 

 Heim, and concludes that " earthquakes seem 

 to be like stifled eruptions which do not find 

 an outlet, about as Dolomieu thought." 



themselves there is now no volcanic action 

 whatever, nor has there been any of significant 

 extent at any time in their geological histor}', so 

 far as it is known. It is altogether gratuitous 

 to suppose that the frequent tremors felt there 

 result from concealed volcanic explosions ; for 

 they find sufficient explanation in the forces 

 that have made the mountains, which are un- 

 doubtedly still growing. 



One of the chief reasons for exaggerating 

 the value of the volcanic to the neglect of the 

 orogenic theory has been the improper reading 

 of earthquake maps. The map constructed by 

 Mallet in 1858, still the best of its kind, is 

 very commonly quoted as showing a general 

 agreement in the distribution of volcanoes and 

 earthquakes ; but it is quite unwarrantable to 

 include the well-shaken regions of Spain or the 

 Alps, for example, in the volcanic district of 

 the Mediterranean. The shocks of demon- 

 strably volcanic origin seldom extend far from 

 their centres : the eruptions of Italy do not 

 disturb the adjacent countries. In the Alps 



No. 109. — 1885. 



Another cause for the former neglect of the 

 orogenic theory was the almost universal belief 

 that mountain ranges had been lifted up or 

 burst out by expansive force from beneath, 

 instead of squeezed and crushed together by 

 lateral compression, as is now widely accepted. 

 The difference has been concisely expressed by 

 Stur of Vienna : formerly it was ' gebirgshub ; ' 

 now it is ' gebirgsschub.' Of course, as long 

 as geologists were generally of the mind that 

 mountains were produced by uplift from be- 

 neath, it was natural to associate surface 

 shocks with smothered volcanic action, whether 

 eruptions followed or not; but, with the disap- 

 pearance of the idea of uplift as applied to 

 mountain ranges, it is as natural to refer earth- 

 tremors in non-volcanic mountain regions to 

 the crushing forces that produce the disor- 

 dered mountain structure. There is, indeed, 

 now sometimes seen a disposition to go, per- 

 haps, too far in this reaction, and exclude vol- 

 canic action from nearly all share in causing 

 earthquakes. Some of the English observers 

 in Japan, a volcanic region par excellence, are 

 of this mind, and attribute the numerous small 

 shocks, even there, to structural and not to 

 volcanic disturbance. It is a difficult matter 

 to decide. Indeed, the study of earthquakes 

 must, in great part, long remain in a two- 

 thirds condition. Observations are plentiful, 

 hypotheses have never been lacking ; but veri- 

 fication can hardly ever be attained. 



The lack of final and convincing verification 



