Doris Lessing uses the contrast between the safe beach and the rocky beach as a symbol of Jerry's different experiences between each. The safe beach is where mom sits calmly relaxing and soaking in the son. The rocky beach, however, has jagged, pointy, and sharp rocks amidst large dark boulders and walls of rock. The rocky beach is a place for Jerry--eleven years old--to explore and be without his mother's supervision.
Once Jerry is there, a group of native boys show up to dive into the pool found within the rocks. This place is described as a "well of blue sea between rough, pointed rocks." Jerry is then shown by the biggest boy how to dive down in one part of the pool and show up on the other side next to "a big dark rock." Jerry dives down to investigate and sees a large, long black wall of rock under water and that figures that the boy must have swam through a hole in the rock to get to the other side of the pool.
The pointed rocks, the big black boulders, and the wall of rock all represent physical obstacles that Jerry must pass in this tale about a rite of passage. The obstacles are big and intimidating--even dangerous-- but if Jerry can conquer them, the water, the tunnel, then he will be a man. As Jerry later realizes as he goes through the tunnel, the tunnel is tight, sharp and rocky just like the environment around it. The tunnel is not safe, slick or smooth. It is dangerously sharp and dangerous.