1869.] HUNT — ON VOLCANOES AND EARTHQUAKES. 391 



The continents, with the exception of the two areas already 

 defined, present no evidences of modern volcanic action, and the 

 regions of ancient volcanic activity, as shown by the presence of 

 great outbursts of eruptive rocks, are not less limited and 

 circumscribed. In northern Europe, the chain of the Urals, an 

 area in central Germany, and one in the British islands are 

 apparent, and in North America there appear to have been but 

 two volcanic regions in the paleozoic period — one in the basin of 

 Lake Superior, and another, which may be described as occurring 

 along either side of the Apallachian chain to the north-east, 

 including the valleys of the lower St. Lawrence, Lake Champlain, 

 the Hudson and Connecticut rivers, and extending still farther 

 southward. The study of the various eruptive rocks of this 

 region shows that volcanic activity in different parts of it was 

 prolonged from the beginning of the paleozoic period till after 

 its close. 



Having thus before us the principal facts in the history of 

 volcanoes, we may proceed to notice the various theories from 

 time to time put forward to account for them. The first and 

 most obvious notion is that of combustion, and we find early 

 writers supposing that volcanoes might be due to the burning of 

 coal, bitumen, or sulphur. As juster ideas were acquired of the 

 nature of combustion, and the necessity of a supply of air for its 

 maintenance, other chemical agencies were invoked as the probable 

 source of internal fire. Lemery suggested the oxidation of 

 sulpliurets in the presence of water, and the brilliant discovery by 

 Davy, in the earths and alkalies, of metallic bases which decom- 

 pose water with great violence, and even with the phenomena of 

 combustion, gave rise to the so-called chemical theory of volcanoes, 

 which has found its defenders down to our own time. This 

 theory supposes that the interior of the globe consists of the 

 metallic bases of earths and alkalies, which are oxidized by the 

 gradual access of the ocean's water, with the production of intense 

 heat, causing the fusion of the resulting oxides, which constitute 

 lavas and eruptive rocks. The chemical objections which maybe 

 urged against this theory are numerous, and to my mind insuper- 

 able ; in addition to which it may be added that it fjiils to explain 

 the facts connected with the past and present distribution of 

 volcanoes, and is in disaccord with those views of the early condi- 

 tion of the globe most in harmony with the deductions of modern 

 astronomy, physics, and chemistry. 



