1886.] NEW YOEK ACADEMY OE SCIENCES. 27 



feature in the Sout h Carolina earthquake, but this is a phenom- 

 enon common to many earthquakes, and is specially noticed in 

 the accounts we have of those of Newburyport of 1727, and 

 New Madrid, 1811. It is, doubtless, due to the pressure 

 exerted by the earthquake-wave on subterranean reservoirs of 

 water, or the compression of water-bearing strata. 



Another circumstance, which has excited some curiosity, is 

 the twisting of chimneys and monuments on their foundations. 

 This has been noticed among the consequences of many earth- 

 quakes, and it has been generally attributed to a gyratory move- 

 ment of the earth, but Mr. Mallet has shown that this is not a 

 necessary conclusion, but that an adhesion to one part of the 

 foundation would cause a revolution of the superstructure abouc 

 this point. 



It will be noticed that, in the reports which have been given 

 of the Charleston earthquake, there is an absence of all refer- 

 ence to the explosions which have been among the most striking 

 and destructive phenomena of earthquake action in some locali- 

 ties. Thus, in the description of the great earthquake of Eio- 

 bamba, Equador, in which 40,000 persons perished, it is said 

 that the bodies of many of the inhabitants were thrown upon a 

 hill which rose to the height of 100 feet on the other side of a 

 stream; and, during the earthquake of Chili, 1837, a mast, 

 planted 30 feet deep, was thrown out so that a round hole re- 

 mained behind. These, which are called explosive earthquakes, 

 have been confined to the vicinity of volcanoes and to districts 

 bordering on the sea, and it is supposed that, by the disruption 

 of the rocks, large quantities of water have been suddenly 

 brought into contact with melted lava. Steam has played an 

 important part in most volcanic eruptions, though as a second- 

 ary, and not, as often supposed, a primary cause. Masses of 

 molten matter, Avelling up through fissures in the earth's crust, 

 must necessarily come in contact with subterrean reservoirs of 

 water, or with strata saturated with moisture. In the vicinity 

 of tiie sea, too, where most volcanoes are located, water may be 

 admitted in the manner just described. In all these cases, 

 steam would be generated in such quantities as to make this an 

 efficient adjuvant to the lava flood in producing disruption, up- 

 heaval, and vibrations of the rocks. The absence of these vio- 

 lent features in the earthquakes of the country bordering the 

 Alleghany belt proves that volcanic action has had nothing to 

 do with them, and shows that, like a vast majority of earth- 

 quakes elsewhere, these have been, as Dana says, "incidental 

 phenomena in the process of mountain building;'' that is, they 

 are sensible signs of the lateral movement of the earth's crust 

 which results in the crushing, folding, faulting, elevation, and 



