What did Karana use to get a canoe off a high cliff without ruining it?

From the text:

Of the four canoes stored there against the cliff, I chose the smallest, which was still very heavy because it could carry six
people. The task that faced me was to push it down the rocky shore and into the water, a distance four or five times its length. This I did by first removing all the large rocks in front of the canoe. I then filled in all these holes with pebbles and along this path laid down long strips of kelp, making a slippery bed. The shore was steep and once I got the canoe to move with its own weight, it slid down the path and into the water.