He involuntarily grasped it.

It was immovable, and it felt like a tree, a few inches in diameter, standing perpendicularly in the lake.

Wondering what this could be, he took hold of it with his other hand, and finding that it supported him, he let his feet drop, when, to his surprise, he found that they rested on something with a rounded surface, and the idea instantly came into his mind that it was a submerged tree, the trunk lying horizontally, from which this upright branch projected.

This might be as good a resting-place as the rock to which he had been going, and standing on it, with his head well out of the water, he turned to speak to Ralph.

At that moment his feet slipped from the slimy object on which he stood, and he fell backward into the water, still grasping, however, his upright support.