100 CARBONIFEROUS LIMESTONES OF IOWA. 
ever, for a short distance, on the Upper Rapids of the Mississippi, charged with 
Pecopteris (Table VI. Fig. 7), and other fossil plants. On these Rapids, near the head 
of Smith’s Island, the carboniferous rocks finally give place to Magnesian Lime- 
stones of Upper Silurian date. 
CONCRETIONS IN CARBONIFEROUS SANDSTONE, MUSCATINE. 
SECTION V. 
THEIR PHYSICAL AND AGRICULTURAL CHARACTER. 
Tur carboniferous rocks of Iowa occupy a region of country, which, taken as a 
whole, is one of the most fertile in the United States. No country can present to 
the farmer greater facilities for subduing, in a short time, wild land. Its native 
prairies are fields, almost ready made to his hands. Its rich, black soil, scarcely 
less productive than that of the Cedar Valley, returns him reward for his labour a 
hundred-fold. The only drawback to its productiveness is that, on some of the 
higher grounds, the soil, partaking of the mixed character common to drift soils, is 
occasionally gravelly; and that, here and there, where the upper members of the 
coal-measures prevail, it becomes somewhat too siliceous. 
The rural beauty of this portion of Iowa can hardly be surpassed. Undulating 
prairies, interspersed with open groves of timber, and watered with pebbly or rocky- 
bedded streams, pure and transparent; hills, of moderate height and gentle slope ; 
here and there, especially towards the heads of the streams, small lakes, as clear as 
the rivers, some skirted with timber, some with banks formed by the greensward 
of the open prairie ;—these are the ordinary features of the pastoral landscape. 
For centuries, the sucessive natural crops of grass, untouched by the scythe, and 
but very partially kept down by the pasturage of buffalo and other herbivorous 
animals, have accumulated organic matter on the surface soil to such an extent, 
that a long succession, even of exhausting crops, will not materially impoverish the 
