Along the strand of an island he passed there was a dark line like a stain, and in still water under the lee the surface was covered with a floating scum.

Felix, on seeing this, at once concluded that he had unknowingly entered a gulf, and had left the main Lake, for the only place he had ever seen scum before was at the extremity of a creek near home, where the water was partly stagnant on a marshy level.
The water of the Lake was proverbial for its purity and clearness.
He kept, therefore, a sharp look-out, expecting every moment to sight the end of the gulf or creek in which he supposed himself sailing, so that he might be ready to lower his sail.

By degrees the wind had risen till it now blew with fury, but the numerous sandflats so broke up the waves that he found no inconvenience from them.

One solitary gull passed over at a great height, flying steadily westwards against the wind.

The canoe now began to overtake fragments of scum drifting before the wind, and rising up and down on the ripples.