Page:The fairy tales of science.djvu/335

Rh of the Supreme Intelligence it is, which has left open to King Pluto these ready means of forcing an outlet; and man ought to feel rather thankful when he beholds the flaming head of the Fire King towering above the crater of some volcano. Earthquakes surely are much more terrible and destructive than volcanic eruptions.

A volcano may be defined as a perpendicular tunnel in the earth’s crust, through which heated matter from below is thrown up to the surface. The matter thrown up may be in the form of lava, scoriæ, ashes, mud, &c. The tunnel or fissure is generally called the chimney, vent, or chasm of the volcano. The upper part of the chimney is called the crater; it always presents the form of an inverted cone, or the shape of a funnel with the broad part upward. A distinction is made between so-called craters of eruption and craters of elevation.

Craters of eruption are formed by the boiling streams of lava, the floods of hot mud, or tuf, and the showers of ashes and cinders gathering or falling around the mouth of the vent or chimney of a volcano. In proportion to the continuance of the eruption, and its repetition, successive beds of volcanic products will accumulate round the mouth, and form themselves into the shape of a sugar-loaf or cone.

Craters of elevation, on the other hand, are formed by the matter of the volcanic eruption lifting the horizontal strata in which the crater is formed, until