- A depression of small extent when steep-sided is termed a " caldron," and a long narrow depression crossing a part of the continental border is termed a " furrow."
- Rictiovarus in disgust cast himself into the fire, or the caldron of boiling tar, from which they had emerged refreshed.
- Near the centre of the park is Mud Caldron, a circular crater about 40 ft.
- Similarly we may note the caldron or small steep depression of a round outline, and the furrow or long narrow groove in the continental shelf.
- The Baltic Sea exceeds 50 fathoms in few places except the broad central portion, though small caldron-like depressions here and there may sink below zoo fathoms. The Red Sea on the other hand, though shut off from the Indian Ocean by shallows of the Strait of Bab-elMandeb with little more than ioo fathoms, sinks to a very considerable depth in its central trough, which reaches 1209 fathoms in 20° N.