190 NATUEAL HISTOEY BULLETIN 



They extend in a northeasterly direction. They were formerly 

 well forested and still show more or less timber on their rounded 

 slopes. Figure 2 shows the much more rugged and abrupt bluffs 

 on the Iowa side above jMissouri Valley, looking north, almost 

 opposite those shown in figure 1. They are fully exposed to the 

 southwest and are covered with a typical prairie flora. 



The two views on plate VI show opposite sides of a valley which 

 branches off from the main Missouri valley in a northeasterly di- 

 rection north of Turin, Iowa. The views were taken from the 

 same point, figure 1 looking southeast at the exposed prairie side, 

 and figure 2 looking southwest at the sheltered forested side. 



Plate VII presents two views taken just north of Missouri 

 Valley. Figure 1 shows the bluffs of the main valley, looking 

 north. They are here exposed to the southwest, and are covered 

 with a typical prairie flora. The Harrison county plants in- 

 cluded in colunm III of the table of plants were collected here. 

 Evaporation station 3 was located on the prominent point at the 

 north end of the bluffs. The view in figure 2 was taken from the 

 top of the same ridge, looking northeast, and shows the strongly 

 contrasting interior wooded valley known as Snyder's Hollow. 

 This valley has a narrow entrance and is well sheltered by the 

 ridge shoAvn in figure 1. The area shown in plate IX, figure 2 

 is a part of this sheltered tract. 



The foregoing illustrations were all taken from the loess region 

 of western Iowa, but abundant illustrations may be found on 

 other formations. 



Thus plate III, figure 1, shows a portion of the rough Kansan 

 drift surface in the southwestern part of Lyon county, Iowa. 

 looking almost due east. To the right the valley is sheltered by a 

 great ridge of Kansan extending almost east and west, and caus- 

 ing a deflection of the Big Sioux river almost due west. A forest 

 has developed in the shelter of this great ridge, on its northern 

 slope, and the border of this forested area is shown in the figure. 

 In the lower part of the sheltered valley the trees, belonging to 

 twenty or thirty species, are well-developed, but as they ascend 

 the species become fewer and the individuals more stunted, until 

 the uppermost, or border portions contain only the dwarf bur- 

 oak, Quercus macrocarpa var. olivceformis, which here often 



