A few miles above Vien Chan, the Mekong flows definitively between two rows of hills which narrow and dominate its bed on all sides. Its waters, which until then had unfolded peacefully, forming capricious meanders, on the vast plateau of central Laos, accelerate their course and bubble in the midst of the rocks. The noble river, which sometimes counted its width by kilometers, now surrounded by two barriers whose elevation is constantly increasing, is entirely contained in a ditch which rarely reaches 5 to 600 meters in width, and of which it never manages to get out. At low water, it even occupies only a tiny fraction of this space, and its bed presents only an uneven and tormented rocky surface, a grandiose mosaic where we meet samples of all kinds. the metamorphic formations, marbles, schists, serpentines, even jades, curiously colored and sometimes admirably polished. In the center, a narrow fissure, a sort of canal whose width is sometimes reduced to 40 meters, but whose depth reaches more than 100, contains all the water of the river, which flows there impetuously between two walls of rocks completely sheer.
Garnier, Vol. 1: 293