Rocky Mountains. 387 



their rise and through which they flow. In the valley of the 

 Ohio, the quality of the soil appears to improve, from its 

 source downward. The alluvion of which it is composed, is 

 supplied by the Alleghany and Monongahela rivers, which 

 have their origin and courses in a hilly and mountainous 

 country, possessed in general of a sandy surface. The allu- 

 vion supplied by other tril)utanes, entering the Ohio at va- 

 rious points between its source and its mouth, is of a better 

 quality, being composed principally of argillaceous and cal- 

 careous earth, which are prevailing ingredients in the soil of 

 the country drained by those tributaries. 



It should be remarked, however, in relation to all the va- 

 rieties of alluvia, that they are partially composed of the fine 

 particles of decayed vegetable matter, with which the water 

 drained from the surface of the ground is invariably charged. 

 This property, in alluvial deposits, often prevails to such a 

 degree as to render soils apparently bandy and sterile, re- 

 markablv productive. The alluvial bottoms throughout the 

 United States afford innumerable examples of this fact. The 

 fertilizing principle is no doubt partially contained in the 

 slimy deposits left upon the surface of the ground after an 

 inundation, essentially contributing to the fecundity of the 

 soil. 



The most extensive tract of valley country east of the 

 Mississippi, is that situated within the bluffs of this river, 

 usually denominatf-d the American bottom, extending from 

 the mouth of the Ocoa or Kaskaskias river, northwardly to 

 that of the Missouri. This spacious bottom, although at 

 present elevated much above the range of the highest fresh- 

 ets, is nevertheless alluvial. Its length along the Mississip- 

 pi is about eiffhty, and its average breadth about four miles. 

 It is generally destitute of a timber growth, excejit along the 

 margin of the river, upon which is a skirt of woodland ex- 

 tending almost from one end of the tract to the other. The 

 alluvion of the American bottom is composed of the rich 

 mud brought down by the turbid Missouri, united with an 

 abundance of vegetable matter yielded by the waters of the 

 Upper Mississippi, which also characterizes the bottoms of 

 this extensive river, from the Missouri downward to its 

 mouth. Upon this bottom are situated the town of Kaskas- 

 kia, the villages of Prairie de Rocher, Harrison, Prairie du 

 Pont, Cahokia, and Illinois, together with many other settle- 

 ments. 



On the same side of the river another large tract of valley 



VOL, II. 43 



