Most of the rivers which descend from the western side of the Alleghany mountains are of inconsiderable magnitude, and by no means remarkable, on account of the straightness of their course, or the rapidity of their currents. The maps accompanying this work, will, in the most satisfactory manner, illustrate the great contrast in this respect, between the district now under consideration and the eastern slope of the Rocky Mountains. The Tennessee, the Cumberland, the Kentucky, the Kenhawa and Alleghany rivers, though traversed in their courses by rocky dikes, sometimes compressing their beds into a narrow compass, occasioning rapids, and in other instances causing perpendicular falls, yet compared to the Platte, and the western tributaries of the Missouri generally, can be considered neither shoal nor rapid. Their immediate banks are permanent, often rocky, and the sloping beach covered with trees or shrubs, and the water, except in time of high floods, nearly transparent. The waters of the Ohio, and its tributaries, and perhaps of most other rivers, when they do not suspend such quantities of earthy matter as to destroy their transparency, reflect, from beneath their surface, a greenish colour. This colour has been thought to be, in some instances, occasioned by minute confervas, or other floating plants, or to result from the decomposition of decaying vegetable matter. That it depends on neither of these causes, however, is sufficiently manifest, for when seen by transmitted light, the green waters are usually transparent and colourless. Some rivers of Switzerland, and some of South America, which descend from lofty primitive mountains, consisting of rocks of the most flinty and indestructible composition, covered with perpetual snows, and almost destitute of organic beings, or exuviæ, either animal or {9} vegetable, and whose waters have a temperature, even in summer, raised but a few degrees above the freezing point, which circumstance, together with the rapidity of their currents, render them unfit for the abode of vegetable life, and is incompatible with the existence of putrefaction, notwithstanding the transparency of their waters, and the reddish, or yellowish colour of the rocks which pave their beds, have a tinge of green, like the Ohio and Cumberland, at times of low water. It is well known that the water of the ocean, though more transparent than any other, is usually green near the shores; and on soundings, while at main ocean, its colour is blue. Perhaps the power which transparent waters have of decomposing the solar light, and reflecting principally the green rays, may have some dependence upon the depth of the stratum. If this were the case, we might expect all rivers, equally transparent and of equal depth, to reflect similar colours, which is not always the case.