Verdure and a mild heaven are above; clunking frogs and plants that keep company with man are beneath.
1796, "to make the sound of a cork being pulled from a bottle;" imitative. This was the main sense through most of 19c. Meaning "to hit, strike" is attested from 1940s. Related: Clunked; clunking.
[probably all based on clunk, ''make a dull sound,'' found by 1796]