CHAPTER XVI.
BURIED IN AN UNDERGROUND RIVER.
When Mark felt himself flying from his horse's back through the air, he of course expected to strike heavily on the ground, and nerved himself for the shock.

To his amazement, instead of striking on solid earth he fell into a mass of shrubbery that supported him for a moment, and then gave way.

He grasped wildly at the bushes; but they were torn from his hands, and he felt himself going down, down, down, and in another instant was plunged deep into water that closed over his head.

He came to the surface, stunned and gasping, only to find himself borne rapidly along by a swift current.

He did not for a moment realize the full horror of his situation, and with the natural instinct of a swimmer struck out vigorously.
He had taken but a few strokes when his hand hit a projecting rock, to which he instinctively clung, arresting his further progress.