Alexis Perrey on Earthquakes, 7 
e central nucleus and the crust? And should not the 
presence of these gases modify in some way, the dynamic action 
of the earthquake waves? Is not their sudden explosion, the 
Cause, at times, of transient disturbances in the central mass? 
And, consequently, are there not thence sensible reactions against 
the inner surface of the crust, causing strong vibrations that are 
propagated to the outer surface 
is idea, which I have elsewhere brought forward,’ is re- 
marked upon as follows by the learned author of the Histoire 
des Progrés de la Geologie. ‘As to these immense tempests 
which the author raises at the surface of the incandescent fluid, 
Whose waves of fire beat against the flanks of the mountains 
which project downward like gigantic stalactites, they appear to 
us to be a little remote from the domain of science and to pertain 
rather to that of the imagination.” 
But, without taxing too much the imagination, can we not 
See that these chemical actions, which others have made the sole 
cause of earthquakes, may produce some perturbations, or mod- 
ifications, in earthquake movements which shall obscure at times 
the periodicity ? 
ormerly, especially during the last century, the existence of 
numerous vast caverns in the earth, for the propagation of earth- 
quakes, was admitted. We do not deny the existence of such 
caverns; but, in our view, instead of their favoring earthquake 
vibrations they would arrest, or at least impede, them. The 
simplest break will modify the rate and direction of the undula- 
1ons. But such caverns should also cause, in some cases, mo- 
lecular vibrations which, on being propagated to the earth’s 
surface, would not differ from ordinary earthquakes. The liquid 
Matter, in entering the cavities, would also cause shocks of a 
Similar kind. Hence may come some of those facts registere¢ 
in earthquake tables, which interfere with the exhibition of the 
periodicity. 
We pass by other causes to which earthquakes have been at- 
tributed. Several, although less general than they have been sup- 
posed to be, may be admitted among special or secondary causes. 
* Monss the Scandinavian insula, Ve dela Com- 
reson Besontifqee do ied en Seondinavic, en Lapua, ea, Pars, 1845. 
