The method of travelling was for Powell to go ahead in the Emma Dean to examine the nature of each rapid before the other boats should come down to it.

If he saw a clear chute he ran through and signalled "come on," but if he thought it too risky he signalled "land," and the place was examined as well as he was able from the shore.

If this investigation showed a great many dangerous rocks, or any other dangerous element, a portage was made, or the boats were let down along the edge by lines without taking out the cargoes.

In this careful way they were getting along very well, when one day they came to a particularly threatening place.

Powell immediately perceived the danger, and, landing, signalled the other boats to do likewise.