210 On Earthquakes — their causes and effects. 



generally seen in connexion with an eruption of the vol- 

 cano, but.it is called into action by the unusual excitement 

 of heat, and is therefore an elfect and not a cause. Dolo- 

 mieu denies the agency of electricity; he says, " J'exclue 

 I'electricite, qui ne pent pas s'accumuler, constamment pen- 

 dant un an de suite, dans un pais environne d'eau, ou tout 

 concourt a mcttre ce fluide en equilibrc. ]| me reste le 

 feu." 



When we undertake to give a history of the eruptive state 

 ©f the bowels of the earth, we must commence that history 

 with the actual existence of their inflamed state ; for, al- 

 though many volcanoes (which may be termed pores or 

 eruptive canals of the earth) arc not in an active state, and 

 have been slumbering for hundreds of years, yet we have 

 others that are seldom or never dormant — that of Stromboli 

 has been throwing out unremitted flames for two thousand 

 years. 



The earliest historians have given relations of many earth- 

 ♦juakes. Those of Pliny are among the best authenticated. 

 In A. D. 79, Herculaneum was covered with lava seventy 

 feet thick. Notwithstanding this continued ebullition, we 

 find the surface of the earth but little changed by this agent, 

 except in the immediate vicinity of volcanoes. 



We have very strong reasons to believe that a conside- 

 rable portion of the interior of the earth is in a constant 

 state of incandescence. In South America the bursting 

 forth of one volcano is frequently followed by that of others, 

 in the chain of the Andes at a great distance. So distinctly 

 has this happened, that Humboldt considered this chain com- 

 posed, not of different volcanoes, but of one immense vol- 

 canic wall stretching from north to south. The existence of 

 this being before our eyes, it is easily to be supposed that 

 larger and more extensive channels may exist at greater 

 depths. It is difHcult, the same author says, " not to admit 

 the existence of cavities between the oxided parts of the 

 globe — parts abounding in metalloids." The extensive 

 ranges that earthqiiakes frequently take go far to prove the 

 existence of great channels of communication. Boyle, in the 

 following quotation, expresses this opinion. 



" 'Tis the more likely that this earthquake shook great 

 tracts of land beyond those places to which the fired matter, 

 passing from one cavity to another, could reach in so short a 

 time." — Bor/le, Vol. J. p. '179. 



