Volcanoes. 433 



Ims^ ever been proposed, it is nothing more philosophical than 

 the fable we have mentioned, and far less poetical : but it is 

 not surprising that such a theory as this should have obtained 

 currency among the ancients, for they were almost entirely 

 ignorant of all those facts upon which an explanation of the 

 phenomena of nature must be founded ; and the same reason 

 which is an apology for the ignorance of the moderns upon 

 the cause of volcanoes applies equally to the ancients. The 

 phenomena which accompany eruption prevent a direct exa- 

 mination of its cause; and, consequently, opinions must be 

 formed from the circumstances under which the effect is pro- 

 duced, the extent of the volcanic action, and the character 

 of the ejected mass. With all these the ancients were un- 

 acquainted; but our knowledge is much inferior to our 

 opportunities. 



Werner was among the first of the geologists who ventured 

 to propose a theory of volcanic action. He attributes erup- 

 tion to the ignition of coal and other inflammable substances; 

 and, in support of this hypothesis, Pallas informs us that 

 the ejection of mud by the volcanoes near the Cimmerian 

 Bosphorus was occasioned by the combustion of the coal 

 measures. 



J3rieslak proposed to improve this theory by attributing 

 volcanic phenomena to the ignition of petroleum by sulphuric 

 and phosphoric acids, and, in support of his theory, adduces 

 the presence of these substances in lava. 



As it would be difficult to find, in the present day, an 

 advocate for either of these theories, we shall not stop to 

 disprove them. 



A much more singular theory, and one which has a much 

 greater appearance of probability, was proposed by Sir Hum- 

 phry Davy. After the discovery of the metallic bases of the 

 earths and alkalies, he was induced to imagine that the earth 

 itself might, perhaps, have been originally a globe of metallic 

 alloy. Now, if this had been the primitive condition of the 

 world, the combination of the oxygen of the atmosphere with 

 the metals would, he says, have formed a crust of earthy 

 matter, as a superficial covering, the interior still remaining 

 a deoxidised metallic mass. Now, if water should, by pe- 

 netrating through the crust, reach this metallic mass, a che- 

 mical action would be immediately produced. The oxygen 

 of the water, having a great affinity for the metal, would be 

 liberated from the hydrogen, and a metallic oxide would be 

 formed. This chemical action would cause the disengage- 

 ment of caloric, sufficient to melt the surrounding rocks, 

 while the disengaged hydrogen gas would, exerting its influr 



Vol. VII. — No. 41. ff 



