VOLCANOES. 021 



explained, as it is impossible t6 ascertain positively the cause of volcanic 

 action. Whether the earth is interiorly a mass of molten rock and fire, or 

 whether the heat is created by the intense contractile force and movement 

 of rocks, and their motion thus developed into heat aided by chemical 

 combination, we cannot absolutely determine. The theory restricting volcanic 

 phenomena to the upper crust of the earth, by supposing the local accumu- 

 lations of hot liquid masses of rock, which are forcibly emptied by the 

 expansion of vapours, may perhaps be found the true one. 



The majority of the volcanoes are found near, or at no very great 

 distance from, the sea. We may therefore expect to find that water has 

 something to do with the eruptions as it has in the case of the Geysers. 

 But this hypothesis will scarcely hold good in every case, though volcanoes 

 of later ages are limited to regions very different from those in which volcanic 

 action used to be. For instance, in America we have only volcanoes on the 

 Pacific side, and the Andes furnish several. Mexico, Central America, and 

 California possess many volcanoes, and as far north as Alaska we find 

 Mount Elias. There are plenty of extinct volcanoes in Europe, but the 

 Mediterranean produces the active vents ; and about the Red Sea and the 

 Caspian, and even in the central chain of Asia, there are volcanoes far from 

 water. The Hawaii isles, on the other hand, are all volcanic, and Australasia 

 furnishes us with remarkable specimens ; so altogether the testimony tends 

 to prove that where volcanic remains are apparent the sea had at one time 

 been, or now is, near at hand. 



Burning mountains have been familiar to us from our childhood in 

 pictures, and by stirring narrative of destruction wrought by them. The 

 volcano is generally a mountain rising to a cone, but Vesuvius presented 

 quite the appearance of a hollow basin at the top, before it suddenly broke 

 forth and buried Herculaneum in ashes. Von Buck visited it in 1799, 

 and declares it had at one time risen, like an island, from the sea. There 

 are about two hundred and seventy volcanoes at present in activity ; four in 

 Europe ; eleven in Iceland and Jan Meyen's land ; in Asia, ninety-three ; 

 in Africa, twenty-six ; forty-six in North America and the Aleutian Isles ; 

 twenty-seven in Central America and the Antilles ; in South America, 

 thirty-one ; and twenty-four islands with volcanic tendencies largely deve- 

 loped. There may be many more " resting." 



Volcanoes, then, are openings or vents which communicate with the 

 melted rock within the earth, and the conical form of volcanoes is owing to 

 the deposits of volcanic matter as it falls from the opening called the crater. 

 If we let a small spade full of mould run through our hands, or from the 

 spade, it will form a small, cone, the heavier particles sliding to the base at 

 a certain slope. Thus the volcano builds its own hill, and inside the crater 

 we find cones from which smoke and steam issue. These cones within the 

 cone are the points of issue of vapour and smoke, miniature volcanoes making 

 up a whole. 



The signs of eruptions are much the same, and usually occur a couple 



