One mile below this point (which we call the Falls or the Canadian, rather for the sake of a name than {25} as considering it worthy to be thus designated), is the entrance, from the south, of a river fifty yards wide. Its banks are lined with tall forests of cotton-wood and sycamore, and its bottoms are wide and fertile. Its bed is less choked with sand than that of the river to which it is tributary. Six or eight miles farther down, and on the other side, is the confluence of the Great North Fork, discharging at least three times as much water as we found at the falls above mentioned. It is about eighty yards wide. The beds of both these tributaries are covered with water from shore to shore, but they have gentle currents, and are not deep, and neither of them have in any considerable degree that red tinge which characterizes the Canadian. We have already mentioned that what we consider the sources of the North Fork are situated in the floetz trap country, nearly opposite those of the Purgatory Creek of the Arkansa.[82] Of one of its northern tributaries we have received some information from the recent work of Mr. Nuttall, who crossed it in his journey to the Great Salt river of Arkansa in 1819.[83] "Still proceeding," says he, "a little to the north of west, about ten miles further, we came to a considerable rivulet of clear and still water, deep enough to swim our horses. This stream was called the Little North Fork (or Branch) of the Canadian, and emptied into the main North Fork of the same river, nearly 200 miles distant, including its meanders, which had been ascended by the trappers of beaver." From his account it appears that the banks of this stream are wooded, and that the "superincumbent rock" is a sandstone, not of the red formation, but probably belonging to a coal district. Its water, like that of the Arkansa, and its northern tributaries, when not swelled by rains, is of a greenish {26} colour. This colouring is sometimes so intense in the rivers of this region as to suggest the idea that the water is filled with minute confervas or other floating plants, but when we see it by transmitted light, as when a portion of it is held in a glass vessel, the colour disappears. Three and a half miles below the confluence of the North Fork is a remarkable rock, standing isolated in the middle of the river, like the Grand Tower in the Mississippi. It is about twenty-five feet high, and fifty or sixty in diameter, and its sides so perpendicular as to render the summit inaccessible. It appears to have been broken from a high promontory of gray sandstone overhanging the river on the north side. Not being able to find grass for pasture, we rode later than usual, and were finally compelled to encamp on a sandy beach, which afforded nothing but rushes for our horses.