The Ramsay book cited by Barb is helpful for "crossing." As a navigation term it means exactly that, and the examples cited by Ramsay indicate some crossings were easily seen by the ripples in the current while other required complicated mapping on the navigation charts. "Crossing-marks" were used to show the location of those not so easily seen from the surface behavior of the water. But because the channel location changed (along with points) they are closely related as navigation terms because they tend to occur (and change) in conjunction with each other. But the geographical and navigational meaning of "point" is very nearly the same; the meanings for "crossing" are not. Thanks go to Barb for citing Robert Ramsay's work. I have a dozen steamboating reference books, most with glossaries, but they do not all agree, and they certainly do not all agree with Ramsay, who provides numerous citations providing the context in which Twain used the terms. Steamboat jargon was the subject of hot debate in Twain's day. I have his own copy of a steamboating novel in which he wrote withering critical comments on the misuse of the jargon on nearly every page in the first 30 pages of the book, and I've read a contemporary steamboating history that regarded Twain as ill-informed and incompetent. Kevin Mac Donnell Austin TX