380 SEE— THE NEW THEORY OF EARTHQUAKES [November 15 



of the earth. Thus subterranean steam would arise beneath the 

 crust and accumulate till relief was afforded by a shaking of the 

 earth, which gave more space for the saturated underlying molten 

 rock. Hence arise the earthquake belts near the deep seas, where 

 easy relief becomes established in the neighboring crust as it is 

 gradually uplifted into a great ridge or mountain chain. 



§ 8. Explanation of the Instability of Steep Slopes near Deep 

 Seas Noticed by Seismologists. — Montessus de Ballore and Pro- 

 fessor Milne both dwell on the instability of steep slopes near deep 

 seas. The meaning of this is now plain ; namely, the slopes become 

 steep by the uplifts due to the expulsion of lava from beneath the 

 deep seas, and the seismic instability arises from this expulsion of 

 lava under the land. The converse proposition for shallow seas 

 is obvious enough, and well illustrated almost ^tU over the world. 

 In some places relief goes on after the seas have become shallow, 

 but there can be scarcely any doubt that the movement started when 

 the water was deeper than it is now. The zvorld as we find it 

 represents the cumulative effects of physical causes zvorking over 

 vast periods of geological time. And our best rule is to study the 

 typical processes where the zvater is deep, and the undermining 

 and upheaval so plain as to admit of no doubt. In time we m^ay 

 be able to trace out the history of other unstable regions nozu in 

 shallozv zvater, or even above the sea l^vel. No one would now 

 expect to see a range of mountains form far inland, and where such 

 ranges now stand the bed of the sea once encroached. In the course 

 of time the details in the development of such ranges will no doubt 

 be fully worked out, but geology is not yet sufficiently advanced to 

 unravel all that is hidden in the crumpling and folding of the earth's 

 crust. The progress of the next two centuries ought to enable us 

 to write a fairly accurate history of the development of the earth. 

 All the details of particular regions now being gathered would be 

 unintelligible unless analyzed by means of correct underlying prin- 

 ciples, and as these have only been established very recently, we 

 content ourselves with outlining correct general ideas, and illus- 

 trating the true physicial cause by a few cases which are beyond 

 question. More cases can be added when our knowledge of the 

 world is more developed; but it may require the work of several 



