Which preposition to use with lipper

of Occurrences 2%

Twenty times did each fancy that he saw the dark back, or head, of the object he sought; but as often did it prove to be no more than a lipper of water, rolling up into a hummock ere it broke, or melted away again into the general mass of the unquiet ocean.

at Occurrences 1%

I could catch the rustle of the water on the beachnot of any waves, for the bay was smooth as glass, but just a lipper at the fringe; and wishing to put off with any excuse the descent into the passage, though I had quite resolved to make it, I settled with myself that I would count the water wash twenty times, and at the twentieth would let myself down into the hole.

Which preposition to use with  lipper