THE PEAIEIES IQI 



fruits before it has reached the height of one foot. But even this 

 hardy xeroph^i:e cannot resist the southwesterly winds and sun 

 and it runs out before reaching the exposed top of the great ridge 

 which is likewise covered with a tj^pical prairie flora. The effect 

 is exactly the same as on the loess ridges. 



Another interesting illustration is shown in plate II. figure 1, 

 This view was taken looking northeast near Reno. Minnesota, and 

 shows the treeless exposed rock and geest-covered southwesterly 

 surfaces. These exposed surfaces were covered with a prairie 

 flora, while the sheltered forested areas showed a typical forest 

 flora. 



Similar illustrations may be observed on all the geological form- 

 ations which form the surface soil in the rougher parts of the 

 prairie states. In Iowa, as already noted, the distribution of 

 forest and prairie is independent of geological formations except- 

 ing in so far as the latter determine topography. This is illus- 

 trated by the forest map^ (plate XIT) which shows the distri- 

 bution of the original forest and prairie areas in Iowa, the former 

 being represented in black. 



It will be noticed that the forests were found chiefly in the 

 northeastern, southeastern and south-central parts of the state, 

 and usually adjacent to the larger streams. The latter fact gives 

 color to the view that the proximity of the stream is directly re- 

 sponsible for the forest, but not only were groves found at points 

 remote from streams, as in the extreme northeastern part of the 

 state and elsewhere, but many streams were entirely destitute of 

 the forest border. This was and is especially true of the upper 

 courses of the streams in the north-central part of the state, and 

 of practically all the streams which empty into the ^lissouri river. 



The explanation of the absence of forests from the vicinity 

 of these streams is again evidently to be found in peculiarities of 

 topography. The north-central part of the state is occupied by 

 the Wisconsin drift area the limits of which are indicated on the 

 map by the heayv line drawn from Osceola through Dallas to 

 "Worth counties. This is a flat plain into which the larger streams 

 have cut narrow valleys which form the only variation in the to- 



' Originally published in the Proceedings of the loTva Academv of Sci- 

 ences, vol. YII, 1S99. 



