172 NATURAL HISTORY BULLETIX 



Newberry, D. D. Owen, Shaler, Upham, Worthen, and other well- 

 known geologists wrestled with it with varying success. White 

 specially states* that the '"question of the origin of the prairie 

 has become more hackneyed perhaps, than any other of the specu- 

 lative questions which North American geology affords," and 

 Willard says'^ that "their explanation belongs to the science of 

 Landscape Geology." 



Yet the problem is one which belongs in its most striking as- 

 pects to plant ecology and falls properly within the province of 

 the botanist, for no matter what may be the variation in the sur- 

 face characteristics of the prairies there is comparative unifor- 

 mity in the nature of their floral covering. Not only are prai- 

 ries striking because of the absence of trees, but they are marked 

 none the less definitely by the presence of a flora which is wholly 

 distinct from the smaller (chiefly herbaceous) flora of the forest. 



The areas which were originally covered with a prairie flora 

 in Iowa are of six more or less distinct types : 



1. The broad flat plains which characterized the Wisconsin 

 (see plate I, figure 1) and lowan drift areas and a part of the 

 un-eroded Kansan drift area such as may be observed in Osceola 

 county and southward. These plains contained large undrained 

 areas, the swamps, ponds and lakes of which possessed a rich 

 hydrophytic flora the discussion of which does not fall within 

 the limits of this paper. 



2. The more rolling drift surfaces such as are presented by 

 the greater part of the Kansan area and the more or less distinct 

 moraines bordering the Wisconsin and lowan areas." A part of 

 the Kansan area is covered with a rather thin veneer of loess. 



3. The very rough loess ridges which border the Missouri val- 

 ley and which present the most extreme xerophytic conditions 

 in Iowa. Similar conditions are found in the rough Wisconsin 

 morainic ( ?) region in southwestern Lyon county, and the floras 

 of the two areas are practically identical. (See plate III; plate 

 IV. fig. 2; plate V, fig. 1; and plate VIL fig. 1). 



•tReport on the Geological Survey of Iowa, Yol. I, 1870, p. 132. 

 ■ Willard, Daniel E., The Story of the Prairies, 1903, p. 21. 

 6For the distribution of the drift areas in Iowa see map, plate III. 

 Report of Iowa Geological Survey, Yol. XIY, 1904. 



