London's description of Buck's rescue of Thorton when he was downing in the rapids?

Here is an excerpt from the book. If there is anything particular you need, let me know.

Buck had sprung in on the instant; and at the end of three hundred yards, amid a mad swirl of water, he overhauled Thornton. When he felt him grasp his tail, Buck headed for the bank, swimming with all his splendid strength. But the progress shoreward was slow; the progress down-stream amazingly rapid. From below came the fatal roaring where the wild current went wilder and was rent in shreds and spray by the rocks which thrust through like the teeth of an enormous comb. The suck of the water as it took the beginning of the last steep pitch was frightful, and Thornton knew that the shore was impossible. He scraped furiously over a rock, bruised across a second, and struck a third with crushing force. He clutched its slippery top with both hands, releasing Buck, and above the roar of the churning water shouted: "Go, Buck! Go!"