We flew along for a while, then slackened steam and went cautiously gliding toward the spark.

Presently Mr.Thornburg exclaimed-- 'Hello, the buoy-lantern's out!' He stopped the engines.

A moment or two later he said-- 'Why, there it is again!' So he came ahead on the engines once more, and rang for the leads.
Gradually the water shoaled up, and then began to deepen again! Mr.
Thornburg muttered-- 'Well, I don't understand this.

I believe that buoy has drifted off the reef.

Seems to be a little too far to the left.