EXPLANATION OF PLATES 



Plate I — Beach and bars. 



Fig. 1 — Sand beach on the south side of Gull Point on West Okoboji 

 lake. The ridge to the left was formed by ice during the pre- 

 ceding winter. August, 1916. 



Fig. 2 — Sand and mud bar of the Missouri river soon after its forma- 

 tion by a flood. Harrison county, Iowa. 



Fig. 3 — The same bar a year later. Covered largely with young Salix 

 longifolia. 



Plate II — Sand dunes. 



Fig. 1 — A new dune near the Missouri river. West of Missouri Valley, 

 Iowa. 



Fig. 2 — A somewhat older dune among the eottonwoods, in the same 

 locality. 



Fig. 3 — An old dune, now covered with Salix missouriensis and various 

 prairie and sand species, in the same locality. The dunes and 

 sand flats in the background are covered with a still alder Cot- 

 tonwood forest. The U. S. survey of 1853 shows that this part 

 was occupied by the Missouri river at that time. 



Plate III — Harrison county sand areas. 



Fig. 1 — A part of the forest shown in the preceding figure. 

 Fig. 2 — A dune which had been held by Salix amygdaloides, but is now 

 breaking down. 



Fig. 3 — A Cottonwood with roots exposed by the blowing away of the 

 sand. 



Plate IV — Muscatine county dunes. 



Fig. 1 — A bare surface at the north end of the Big Mound, with Gledit- 



sia triacanthos (dwarfed) in the background. 

 Fig. 2 — North end of Big Mound, with bare surfaces, shifting. 

 Fig. 3 — Dune on Big Mound which has nearly covered a fence; buried 



posts show at right. At left is part of a newer fence. 



Plate V — Muscatine county dunes. 



Fig. 1 — Old dune in background, with a small "blow out." The soil in 



the cornfield is also very sandy. Quercus velutina is abundant 



in the sandy soil in background. 

 Fig. 2 — Mollugo verticillata on blown out part of dune in fig. 1. 

 Fig. 3 — Old sandy slope on Big Mound, now covered with prairie plants. 



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