CHEMISTRY OF THE EARTH. 205 



wider sense, a inauifestatiou of viilcauicity, aud for the elucidation of our ' 

 subject consider both those regions characterized by great outbursts of 

 phitonic rock in former geologic periods aud those now the seats of vol- 

 canic activity, which, in these cases, can generally be traced back some 

 distance into the tertiary epoch. To begin with the latter, the first aud 

 most important is the great continental region which may be described 

 as including the ^lediterranean and Aralo-Caspian basins, extending- 

 from the Iberian Peninsula eastward to the Thian-Chan Mountains of 

 Central Asia. In this great belt, extending- over about ninety degrees 

 of longitude, are included all the historic volcanoes of the ancient world, 

 to which we must add the extinct volcanoes of ]Murcia, Catalonia, Au- 

 vergne, the Vivarais, the Eifel, Hungary, &c., some of which have pro- 

 bably been active during the human period.* 



Besides the great region just indicated, must be mentioned that of 

 our own Pacific slope, from Fuegia to Alaska, from whence, along the 

 eastern shore of Asia, a line of volcanic activity extends to the terrible 

 burning mountains of the Indian archipelago. Volcanic islands are 

 widely scattered over the Pacific basin, and volcanoes burn amid the 

 thick-ribbed ice of the Antarctic continent. The Atlantic area is in like 

 manner marked by volcanic islands from Jan Mayen and Iceland to the 

 Canaries, the Azores, and the Caribbean Islands, and southward to 

 Ascension, St. Helena, and Tristan d'Acunha. 



§ 51. The continents, with the exception of the two areas already 

 defined, i)resent no evidences of modern volcanic action, and the regions 

 of ancient volcanic activity, as shown by the presence of great out- 

 bursts of eruptive rocks, are not less limited aud circumscribed. In 

 northern Europe the chain of the Urals, an area in central Germany, 

 and one in the British Islands are apparent, and in Xorth America 

 there appear to have been but two volcanic regions in the paleozoic 

 l)eriod — one in the basin of Lake Superior, aud another, which may be 

 described as occurring along either side of the Appalachian chain to the 

 northeast, including the valleys of the lower St. Lawrence, Lake Cham- 

 plain, the Hudson and Connecticut liivers, and extending still further 

 southward. The study of the various eruptive rocks of this region 

 shows that volcanic activity in difi'crent parts of it was prolonged from 

 the beginning of the paleozoic period till after its close. 



§ 52. The theory of Keferstein and Hcrschel, explained in § 37, shows 

 in what manner volcanic phenomena may be directly dependent on the 

 accumulation of sedimentary strata. It has already been shown that 

 both temijerature aud pressure combine to produce in the lower portions 



* It is a most significant fact that this region is nearly co-extensive with that occnpied 

 for ages by the great civilizing races of the world. From the plateau of Central Asia, 

 throughout their westward migration to the pillars of Hercviles, the Indo-European 

 nations were familiar with the volcano and the'earthquake ; and that the Semitic race 

 were not strangers to the same iihenomena, the whole i^oetic imagery of the Hebrew 

 .Scriptures bears amjde evidence. In the language of their writers, the mountains aro 

 molten, they quake and fall down at the presence of the Deity, when the melting tiro 

 burueth. The fury of His wrath is poured forth like fire; He toucheth the hills and 

 tliey smoke ; while fire and suljihur come down to destroy the doomed cities of the 

 ])hiin, whose foundation is a molten flood. Not less does the poetry and the mythology 

 <if Greece and Rome bear the impress of the nether realm of fire in which the volcano 

 and the earthquake have their seat, and their influence is conspicuous throughout the 

 imagiuative literature aud the religious sj'stems of the Indo-European nations, whoso 

 contact with these terrible manifestations of unseen forces beyond their foresight or 

 control could not fail to act strongly on their moral and intellectual development, 

 which would have doubtless presented \ery diflereut phases had the early home of 

 these races been the Australian or the eastern side of the American continent, Avhero 

 volcanoes are unknown aud the earthquake is scarcely felt. (From a lecture before 

 the Amer. Geographical Society, April, 1809.) ■ 



