Two large bowlders that leaned towards each other had stood on top of the ground.

These had been split and shattered into many fragments.

A few pieces, like the one that came so near Cleggett, had been flung to a distance, but for the most part the shivered crowns and broken bulks had been served otherwise; the force of the blast had disintegrated them, but had not scattered them; the greater part of this newly-rent stone had toppled into the fissure in the ground, and lay there mixed with earth, almost filling the hole.
It was impossible to determine just where and how the blast had been set off; the rocks hid the facts.

But Cleggett judged that the force must have come from below the bowlders; mightily smitten from beneath, they had collapsed into the cavern suddenly opening there, as a building might collapse into and fill a cellar.

The pieces that had been thrown high into the air were insignificant in proportion to the great bulk which had settled into the hole and made its origin a mystery.
As Cleggett, bewildered, stood and gazed upon the mass of rock and earth, Cap'n Abernethy gave a cry and pointed at something with his finger.