But if they really do lie under, how can they possibly be of the same age?  One would scarcely venture to suppose, in looking at a building, that the cellars had not been finished before the upper floors.

True.  In the first instance doubtless the cellars were first made, then the ground-floor, then the upper stories.

When, however, the house was so built, alterations and improvements might be very widely carried on above and below.  While one set of workmen were engaged in remodelling the roof, another set of workmen might be engaged in remodelling the kitchens and first floor, pulling down, propping up, and actually rebuilding parts of the lower walls.

This is precisely what the two great fellow-workmen, Fire and Water, are ever doing in the crust of our earth.  And if it be objected that such alterations too widely undertaken might result in slips, cracks, and slidings, of ceilings and walls in the upper stories, I can only say that such catastrophes have been the result of underground alterations in that great building, the earth’s crust....

We see therefore clearly that, although the earliest fire-made rocks may very likely date farther back than the earliest water-made rocks, yet the making of the two kinds has gone on side by side, one below and the other above ground, through all ages up to the present moment.

And just as in the present day water continues its busy work above ground of pulling down and building up, so also fire continues its busy work underground of melting rocks which afterwards cool into new forms, and also of shattering and upheaving parts of the earth-crust.

For there can be no doubt that fiery heat does exist as a mighty power within our earth, though to what extent we are not able to say.

These two fellow-workers in nature have different modes of working.  One we can see on all sides, quietly progressing, demolishing land patiently bit by bit, building up land steadily grain by grain.  The other, though more commonly hidden from sight, is fierce and tumultuous in character, and shows his power in occasional terrific outbursts.

We can scarcely realize what the power is of the imprisoned fiery forces underground, though even we are not without some witness of their existence.  From time to time even our firm land has been felt to tremble with a thrill from some far-off shock; and even in our country is seen the marvel of scalding water pouring unceasingly from deep underground....

Think of the tremendous eruptions of Vesuvius, of Etna, of Hecla, of Mauna Loa.  Think of whole towns crushed and buried, with their thousands of living inhabitants.  Think of rivers of glowing lava streaming up from regions below ground, and pouring along the surface for a distance of forty, fifty, and even sixty miles, as in Iceland and Hawaii.  Think of red-hot cinders flung from a volcano-crater to a height of ten thousand feet.  Think of lakes