EARTHQUAKE PHENOMENA. 359 



more frequent and violent in mountain-regions of recent origin. The 

 Appalachian, which are the oldest mountains in America, are, there- 

 fore, very free from earthquakes, because the rocks have, as a rule, 

 long since relieved themselves ; while, on the other hand, the compara- 

 tively new Rockies are the seat of more frequent tremblings. 



There is a theory for the cause of earthquakes, which is rather 

 neglected by scientific men, but which, I think, will explain many 

 of those phenomena not otherwise accounted for. 



At the mouth of the Ohio, and at Newburyport, Massachusetts, both 

 of which have in times past been the seat of very severe earthquake 

 shocks, the layers of rocks are not badly bent. And, further, I do 

 not see how the theory of bent rocks can explain the frequent repeti- 

 tion of shocks which we have recently seen in Spain, in Newbury- 

 port in 1727, and near the mouth of the Ohio in 1811. These regions 

 had been comparatively quiet for years, and suddenly a severe shock 

 was felt, followed by a series of successive shocks, which, in the case 

 of Spain, have not yet ceased, although the original shock occurred 

 December 24, 1884. The theory, which I have spoken of, and which 

 would explain this, is that there are great quantities of gas accumu- 

 lated at certain points beneath the surface under great pressure, and 

 that this gas, in its attempt to free itself, bursts open the rocks, causing 

 shock after shock, until it has finally relieved itself sufficiently to re- 

 main quiet. This, one will see, is similar to the volcanic theory, except 

 that there is no necessity for the presence of a volcano. What this gas 

 is, does not matter ; it may be accumulations of steam, or it may be 

 evolved from petroleum, or it may be carbonic-dioxide gas evolved by 

 acids working on calcareous rocks. In the Newburyport earthquake, 

 which was the most severe ever recorded in New England, large quan- 

 tities of gas escaped to the surface; and, on the Ohio, gas also escaped. 

 This shock, which was at first wide-spread, finally narrowed itself down 

 to a very limited marshy area and died out. 



To sum up, then, it may be said: 1. That in volcanic regions earth- 

 quakes are a part of an eruption, premonitory warnings ; 2. That in 

 a limestone country the falling in of the walls of caverns may ac- 

 count for some ; 3. That in regions of recent mountain-making the 

 sudden release of tension causes many ; 4. That the pressure of pent- 

 up gases on the surrounding rocks, which are finally burst, may be 

 the cause of a large number, more especially those which are followed 

 by a long-repeated series of shocks ; and, finally, that in any one of 

 these regions either or all of the other causes may (with the excep- 

 tion of volcanic in non-volcanic regions) enter into the production of 

 earthquakes. 



