His eyes fell upon the stone ridge to his left and he thought at first he should build his shelter against the stone. But before that he decided to check out the far side of the ridge and that was where he got lucky. Using the sun and the fact that it rose in the east and set in the west, he decided that the far side was the northern side of the ridge. At one time in the far past it had been scooped by something, probably a glacier, and this scooping had left a kind of sideways bowl, back in under a ledgeIt wasn't very deep, not a cave, but it was smooth and made a perfect roof and he could almost stand in under the ledge. He had to hold his head slightly tipped forward at the front to keep it from hitting die top. Some of the rock that had been scooped out had also been pulverized by the glacial action, turned into sand, and now made a small sand beach that went down to the edge of the water in front and to the right of the overhang. What do "scoop out" mean here?