The internal fires had not yet forced their way through.
But at a later period a wide chasm formed diagonally from south-west to north-east, through which was gradually forced out the trachyte which was to form a mountain chain.

No violence accompanied this change; the matter thrown out was in vast quantities, and the liquid material oozing out from the abysses of the earth slowly spread in extensive plains or in hillocky masses.

To this period belong the felspar, syenites, and porphyries.
But with the help of this outflow the thickness of the crust of the island increased materially, and therefore also its powers of resistance.

It may easily be conceived what vast quantities of elastic gases, what masses of molten matter accumulated beneath its solid surface whilst no exit was practicable after the cooling of the trachytic crust.

Therefore a time would come when the elastic and explosive forces of the imprisoned gases would upheave this ponderous cover and drive out for themselves openings through tall chimneys.
Hence then the volcano would distend and lift up the crust, and then burst through a crater suddenly formed at the summit or thinnest part of the volcano.
To the eruption succeeded other volcanic phenomena.