19211 PALMER, ROTANICAL RECONNAISSANCE OF SOUTHERN ILLINOIS 135 



A low outlying spur of the Ozark uplift crosses the state of Illinois, 

 from the Mississippi to the Ohio River, near its southern extremity. 

 The axis of this ridge passes through the counties of Union, Johnson, 

 Pope and Hardin, and has given rise there to a topography strikingly 

 different from that of the lowlands to the south. Several distinct groups 

 of sedimentary rocks underlie this area. Limestones are most abundant 

 on the western side near the Mississippi River and in Hardin County, 

 bordering the Ohio, while sandstone formations predominate in the central 

 portion and on the northeastern flank. Over much of this area the sur- 

 face is quite rugged, with rock exposures on the ridges and steep hill- 

 sides, and with bold escarpments and bluffs along the streams. While 

 the surface of the highlands is not extensive enough for the formation of 

 large springs, seepage water and small streamlets issue in many places 

 along the bluffs, giving rise to perennial streams in some cases. Al- 

 though rainfall is abundant, owing to the narrowness of the water-shed 

 and the nearness of the two great rivers, none of the streams originating 

 here attain much size. The Cache River, which joins the Ohio a few 

 miles north of Cairo, is the largest of these, and most of the creeks flow- 

 ing south from the central sandstone area unite to form it. Towards 

 their sources many of these small streams have cut deeply into the com- 

 paratively soft, heavily-bedded Tennsylvanian sandstones, forming nar- 

 row gorges with perpendicular or overhanging cliffs, in some cases one 

 hundred to two hundred feet in height. Often deep grottos and rock 

 shelters are found in such places, some of which, where comparatively 

 dry and high enough, were used by the Indians for habitation or refuge, 

 as is shown by the numerous flint chips, fragments of pottery, bones and 

 other debris found near them and by digging in the cave earth of their 

 floors. At other points In the protection of the high cliffs, especially 

 where there is an abundance of moisture and an accumulation of rich 

 soil and humus along the ledges or at the base, a rich flora is established, 

 and some of the trees and herbaceous plants found here arc more typical 

 of the Mounds Formation: amongst these are the Butternut, Tulip 

 Tree, Linden, Sugar Maple and Red and Chinquapin Oaks. More com- 

 mon are the Small Scaly-bark {Canja ovalis) and Tignut Hickory (C. 

 glabra), Black and Schneck's Oak, Black Gum and Red Maple. Along 

 the dry exposed ledges at the top of the bluff there is often a scrubby 



growtl 



(Q 



marilandica) , Tree Huckleberry {Vacciniiaii arhoreum). Winged Elm, 

 Low Hackberry (Ccltis pumila georgiana), and less commonly the June 

 Berry {Amclanchier canadensis) and Fragrant Sumac {Rhus canadensis). 

 Here, too, arc often found such typical barrens plants asOpunf.a humi- 

 fusa. Agave virginica, Crofonopsis elliptica, Talinum calycinum, Hypericum 



gentianoides and Polygonum tenue. 



On the dry uplands Hickories and Oaks constitute a large proportion 

 of the forest. The commonest species are Carya glabra, C. ovalis and 

 its varieties, C. alba, Quercus velutina, Q. alba and Q. skllaia. Shingle 



