PHYSICAL GEOGRAPHY. 5 



growths of pine, and for sovcral years past a great business 

 has been carried on upon the Missisippi in getting lumber 

 down from those regions to the towns along the river. 



The best portions of lliis Upper Missisippi Valley are 

 upon the western shore of Lake Michigan, including the 

 eastern portion of Wisconsin ; the Illinois and Rock rivers, 

 and their tributaries ; the Missisippi on both sides ; and gene- 

 rally the whole of Iowa. In Iowa the prairies are less ex- 

 tensive than in Illinois, and the proportion of wood is greater. 

 In the southern portion of Iowa, below the Iowa River, the 

 soil is more stiff than to the north of that river, where, by a 

 slight admixture of fine sand, it is made more friable and 

 mellow. By reason of this quality, and being also, for the 

 most part, more level, the land south of that river retains its 

 moisture later in the spring, and the soil thus loses the 

 advantage of time which the climate would give in the differ- 

 ence of latitude. 



The soil of the prairie is deeper, and is said also to be 

 richer at a distance from timber than in its vicinity. By 

 scientific examination, it has been found that carbonate of 

 lime enters into its composition in proportion of from twenty 

 to forty per cent. In timber lands the proportion is much 

 less. The first settlers, however, take the timber land for the 

 convenience of fuel and making improvements. Thus the 

 best land is actually the last taken. The soil is of such fer- 

 tility, that in a few years, if the fires are kept out, there will 

 be an abundant growth for all purposes. In the Gazetteer 

 of Missouri, by Dr. Beck, published in 1823, it is stated 

 that St Louis county is generally prairie : yet, in fifteen 

 years after that date, it was almost wholly covered with a 

 thrifty growth of limber. The same is the case with otlier 

 places. 



The following statement of the geological structure of tJial 



