Read it through once

They knew that the time a man could cling to a slippery rock in the face of that driving current was a matter of minutes, and they ran as fast as they could up the bank to a point far above where Thornton was hanging on. They attached the line with which they had been snubbing the boat to Buck’s neck and shoulders, being careful that it should neither strangle him nor impede his swimming, and launched him into the stream. He struck out boldly, but not straight enough into the stream. He discovered the mistake too late, when Thornton was abreast of him and a bare half-dozen strokes away while he was being carried helplessly past.