312 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



Platte river, with its main tributary the North Platte, flows across 

 the state through the central portion from west to east. The width 

 of the North Platte where it enters the state is about five hundred 

 feet, while the width of the Platte at its mouth is more than a mile. 

 The valley of the North Platte is deep and narrow, usually less than 

 half a mile in width, but the valley of the Platte varies in width 

 from one to eight miles. The river banks are low and for the 

 most part are treeless. The water is shallow and in many places 

 divides into several streams which are separated by long sandbars or 

 low wooded islands. 



Niobrara river flows in a narrow gorge for more than two-thirds 

 of its course in Nebraska. The last fifty miles of its course is through 

 a valley varying in width from half a mile to a mile. Here the 

 banks are low and wooded, the blufTs are steep and densely covered 

 with thickets and young trees, and in places the valleys are heavily 

 wooded. 



Republican river enters the state near the southwestern corner, 

 flows eastward through eight counties of the southern tier, then 

 turns southward into Kansas. . The valleys are rather broad and 

 treeless, the bluffs low and bare of trees, in the ravines are willow, 

 Cottonwood and ash trees, the river banks usually have a fringe of 

 willows. The river is broad and shallow with abundant sandbars. 



Big Blue river with its tributaries drains much of the south- 

 eastern portion of the state. The current is slow, the bed and banks 

 are muddy, the valleys are broad, level and rich, and along much of 

 their extent are heavily wooded. 



The fern species that may be found in the river valleys are 

 Osmunda regalis (rarely), Dryopteris thelypteris, and Onoclea sen- 

 sibilis. The fern allies are Equisetum robustum and Equisctiim 

 flitviatilc. 



WOODED BLUFFS REGION 

 'Jhis region consists of narrow strips of country bordering on the 

 river valleys on one side and the uplands on the other. The line of 

 demarcation with the river valley is rather sharp although the woods 

 are in many cases continuous. The separation of the wooded bluffs 

 from the uplands is often not sharply drawn, there being varying 

 degrees of divergence, yet within limits it is distinctive. The 

 wooded bluft's extend in narrow dichotomous strips over much of 

 the state, paralleling the valleys of the main water courses. They 

 reach their greatest development near Missouri river which is the 

 center of their extension westward. Upland woods are an extension 



