10 Expedition to the 



horizontal position, while that of the transition strata has 

 been changed? 



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 Tennes- 

 see, the Cumberland, the Kentucky, the Kenhawa and Alle- 

 ghany rivers, though traversed in their courses by rocky 

 dikes, sometimes compressing their beds into a narrow com- 

 pass, occasioning rapids, and in other instances causing per- 

 pendicular falls, yet compared to the Platte, and the wes- 

 tern tributaries of the Missouri generally, can be consid- 

 ered 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 tributa- 

 ries, 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 mat- 

 ter. 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 exuvige either animal or vegetable, and whose waters 

 hav<; a temperature, even in summer, raised but a few degrees 

 above the freezing point, which circumstance, together with 



