Read it through once

WHEN I returned to the pilot-house St. Louis was gone and I was lost. Here was a piece of river which was all down in my book, but I could make neither head nor tail of it: you understand, it was turned around. I had seen it when coming up-stream, but I had never faced about to see how it looked when it was behind me. My heart broke again, for it was plain that I had got to learn this troublesome river _both ways_.