120 PHYSICAL GEOGRAPHY. 



" No. 5. Ancient soil, two foot thick, very dark brown, resembling the peat but 

 more decomposed. Contains no shells or other fossil remains. 



"No. 6. Blue clay, very tenacious, containing sand, gravel, and small boulders. 

 Pebbles and boulders all water-worn and many of them distinctly glacier 

 scratched. Thickness unknown. 



" The dotted line represents the railroad grade. The point represented by the 

 top of the diagram is 167 above low-water mark in the Mississippi river at the 

 railroad bridge." 



This deposit is quite remarkable in many respects; in none 

 more so perhaps than in the fact that the bed of peat rests 

 npon a bed of clayey silt, and is in turn covered by a similar 

 but much deeper one, these varying conditions evidently 

 having been produced by the shiftings of the adjacent and 

 then sluggish river, in that very early period of its post- 

 glacial history. The extent of this peat bed beneath the 

 surface is not known, as there is nothing in the surrounding 

 surface to indicate it. It was exposed by the railroad exca- 

 vation for a distance of thirty or forty rods. 



Another deposit of ancient peat has been found in digging 

 a well a couple of miles southward from Iowa City. It was 

 found at a depth of thirty feet beneath the surface, and that 

 surface is fifty feet or more below the general level of the 

 uplands in the vicinity, The locality is upon the gentle slope 

 of the valley-side of the Iowa river, and about a mile from 

 it. The position of the peat, although so far beneath the 

 surface, is yet much above the level to which the highest 

 floods of the river now reach. The peat was evidently formed 

 where it is now found, and in what was then a marsh upon 

 the borders of the river-valley as it then existed, but during 

 the process of the deepening of the valley, and by the shift- 

 ings of the stream, it became covered by the sandy deposit 

 which we find now resting upon it, having mostly the 

 general character of Altered Drift. 



Neither this deposit of peat, nor the one near Davenport, 

 are fit for fuel, as they are not nearly so combustible as recent 

 peat, and if they were, they contain too much impurity to be 

 practically useful. Both the deposits contain numerous pieces 



