The hollowed tree became a boat, held together with iron nails.

The boat became a galley, a ship, a paddle-boat, a screw steamer, and the world was opened up for colonization and civilization.
Man would have continued uncivilized, but for the results of the useful labours of those who preceded him.

The soil was reclaimed by his predecessors, and made to grow food for human uses.

They invented tools and fabrics, and we reap the useful results.

They discovered art and science, and we succeed to the useful effects of their labours.
All nature teaches that no good thing which has once been done passes utterly away.