See quot. 1853.
1826. The face of the Mississippi is always turbid; the current every where sweeping and rapid; and it is full of singular boils, where the water, for a quarter of an acre, rises with a strong circular motion, and a kind of hissing noise, forming a convex mass of waters above the common level, which roll down and are incessantly renewed.—T. Flint, ‘Recollections,’ p. 87.
1829. He studied the currents, the boils, and eddies, the marks of shallow and deep water, the indications for steering in the night, and all the hundred complicated physical aspects of this sweeping and dangerous stream.—The same, ‘George Mason,’ p. 124 (Boston). (Italics in the original.)
1853. These “boils,” as the boatmen call them, are immense upheavings of the moving waters [of the Missouri], which rise with a convex surface, sometimes spreading out to near half an acre, and will whirl a loaded flatboat round like a top.—Putnam’s Monthly, ii. p. 188/2 (Aug.).
