236 ILLINOIS ACADEMY OP SCIENCE 



is submitted as a representative part of the forested valley 

 of the Embarrass river. It is a part of the township in 

 which Greenup is situated, township 9 north, range 9 east. 

 The scale of the map is somewhat more than an inch to the 

 mile. The topography is roughly indicated by the bound- 

 ary lines separating flat upland, hill-slopes and bottom- 

 land. The forested areas are not shown on the west side 

 of the river, nor in the ravines at the southern border of 

 the map. The conventions used to denote the several for- 

 est associations are hatched in wherever the forests still 

 stand. The numbers serve to identify them. The type of 

 forest originally present in an area now cleared is indi- 

 cated by its particular number, enclosed in parentheses. 

 Areas formerly or still covered with prairie vegetation are 

 represented by the number 10. Parts of the extensive 

 prairie uplands are shown at the northwest corner and at 

 the eastern border of the map. The general distribution 

 of forest and prairie is shown for the whole county in Map 

 II, on a succeeding page. 



The "ends and corners of uplands in angles between 

 ravines," as mentioned in item 2 of the table, may require 

 brief explanation. These are the flat tops of upland spurs 

 at the valley-border which stand like headlands above the 

 ravines on either side. Their appearance and distribution 

 may be readily seen in Map I, if the reader will follow the 

 line which separates flat uplands from hill-slopes, partic- 

 ularly in section 15. These spur-tops were salients of the 

 prairie areas, closely hemmed in by the forests of the hill- 

 slopes on either side, and in such places the lateral spread 

 of the dry oak forest over the upland surface was initi- 

 ated. This invasion of forest was slow, and, as shown by 

 Gleason, was subject to frequent check and setback by 

 prairie fires, which were far more prevalent on the wind- 

 ward side of stream-valleys. The summer winds in this 

 part of Illinois are mostly from the south, southwest, and 

 west; and one finds that the upland forest belt is wider, 

 and the spur-tops more generally forested, on the leeward, 

 that is, the north, northeast and east sides of streams. This 

 general relation is quite apparent in the soil maps of Cum- 

 berland and other counties in central Illinois. Its result 

 is to make a smoothly curving or nearly straight boundary 

 between prairie and forest, close to the irregular border of 

 the upland on the windward side of the larger valleys, 

 farther from it on the lee side. 



