You take a night when there's one of these grisly, drizzly, gray mists, and then there isn't any particular shape to a shore.

A gray mist would tangle the head of the oldest man that ever lived.

Well, then, different kinds of MOONLIGHT change the shape of the river in different ways.

You see--' 'Oh, don't say any more, please! Have I got to learn the shape of the river according to all these five hundred thousand different ways?
If I tried to carry all that cargo in my head it would make me stoop-shouldered.' 'NO! you only learn THE shape of the river, and you learn it with such absolute certainty that you can always steer by the shape that's IN YOUR HEAD, and never mind the one that's before your eyes.' 'Very well, I'll try it; but after I have learned it can I depend on it.
Will it keep the same form and not go fooling around ?' Before Mr.Bixby could answer, Mr.W---- came in to take the watch, and he said-- 'Bixby, you'll have to look out for President's Island and all that country clear away up above the Old Hen and Chickens.

The banks are caving and the shape of the shores changing like everything.