Twain describes his boyhood in Life on the Mississippi, stating that "there was but one permanent ambition" among his comrades: to be a steamboatman. "Pilot was the grandest position of all. The pilot, even in those days of trivial wages, had a princely salary – from a hundred and fifty to two hundred and fifty dollars a month, and no board to pay. " As Twain described it, the pilot's prestige exceeded that of the captain. The pilot had to "get up a warm personal acquaintanceship with every old snag and one-limbed cottonwood and every obscure wood pile that ornaments the banks of this river for twelve hundred miles; and more than that, must. . . actually know where these things are in the dark". Steamboat pilot Horace E. Bixby took Twain on as a cub pilot to teach him the river between New Orleans and St. Louis for $500 (equivalent to $15,000 in 2019), payable out of Twain's first wages after graduating. Twain studied the Mississippi, learning its landmarks, how to navigate its currents effectively, and how to read the river and its constantly shifting channels, reefs, submerged snags, and rocks that would "tear the life out of the strongest vessel that ever floated". It was more than two years before he received his pilot's license. Piloting also gave him his pen name from "mark twain", the leadsman's cry for a measured river depth of two fathoms (12 feet), which was safe water for a steamboat.