54 IOWA ACADEMY OP SCIENCES. 



southwesterly summer winds, therefore, sweep over this part of 

 the state almost at right angles to the river valleys. Hence 

 the valleys are protected, and this, coupled with a greater 

 rainfall, gives to this part of the state a decided advantage as 

 a tree producer. 



In the Wisconsin drift area most of the streams also flow in 

 a southeasterly direction, and where they have cut deeper val- 

 leys they are freely bordered with timber,* but where no val- 

 leys have been cut the shores and the adjacent plains are 

 almost without exception entirely treeless, f 



In the western part of the state the streams flow in a south- 

 westerly direction, and the southwest summer winds, here more 

 violent th an eastward, sweep them with full force, and pass unhin ■ 

 dered to the flat Wisconsin drift area beyond, which offers prac- 

 tically no obstacles to their progress. And in both these latter 

 regions there are comparatively few trees, and these are mostly 

 stunted, except where a bend in the valley, or a deep lateral 

 ravine affords protection. In this western part of the state 

 the groves are not on the hilltops, but nestle in ravines or on 

 slopes which are on the leeward, north and east side. Even 

 where there are larger tracts of timber, as for example 

 above Hamburg, in Fremont county, and in and near Fairmount 

 park, in Council Bluffs, they are not along the bluffs which 

 face the Missouri river on the Iowa side, but are in the ravines 

 and valleys or on the slopes which lie east of the ridges which 

 form the river bluffs. The Missouri river flows nearly south, 

 and its valley is so broad that the windward, or Iowa, bluffs 

 are fully exposed to the soathwest winds and are treeless, 

 while the opposite protected leeward bluffs of the Nebraska 

 side are for the most part quite heavily timbered. The bur 

 oak which frequently forms the greater part of these western 

 groves, also gives interesting testimony. As generally found 

 in that part of the state it is small and stunted, not more than 

 a foot or two in height, at or near the tops of the ridges, but 

 commonly gradually increases in size down the leeward slopes, 

 the better sheltered trees beiog much larger. J It is claimed 

 by some that the small, stunted oaks near the tops of the ridges 

 owe their small size to the fires which anaually burned the 



*A.s along the Des Moines river in Boone county and northward. 



+As along the upper courses of the forks of the Des Moines river, and along most 

 of the smaller streams in the Wisconsin drift area. 



^Examples are common in Crawford and Carroll counties, and in most of the 

 Missouri river and Big Sioux river counties to the northwestern corner of the state • 



