70 
IOWA ACADEMY OP SCIENCE 
Explanation of Plate V. 
Fig. 1. The northerly slopes of a portion of the Wisconsin drift moraine in south- 
western Lyon county, Iowa, showing more or less forest covering. On these 
slopes there is a distinct soil and a thin loess, while the exposed tops and 
windward slopes are treeless, and without surface soil. (See p. 58.) 
Fig. 2. A sand dune on which plants (chiefly Cassia chaniaecrista) have become estab- 
lished. The dune is now fixed and is beginning to form a finer soil. The 
trees are cottonwoods, and are responsible for the formation of the dune. 
Nearly all the plants on these dunes are leguminose, with abundant root- 
tubercles containing nitrifjfing bacteria. Harrison county, Iowa. (See 
p. 59.) 
