134 JOURNAL OF THE ARNOLD ARBORETUM [vol. ii 



pcfinlatum, Dccodon verfirillatus, Ascleplas percnnis, Dianthera ovafa, 

 Spilauthca nmcricana aiui Mikania scandcns. 



Bordering the Oliio River and extentling almost across the southern 

 extremity of the state, except wlicre interrupted by the broad flood plain 

 of the Cache, there is a narrow area, from three to fifteen miles wide, 

 underlaid by deposits of Tipper Cretaceous age. These consist largely 

 of unconsolidated materials: clay, gravel, sand and loamy residual soil 

 and alluvium. The surface here is marked by low hills with gentle slopes, 

 di.ssected here and tlierc by deep ravines or narrow valleys, where grows 

 a luxuriance of ferns and wild flowers under the cover of shrubbery and 

 trees that clothe their steep sides. Where uncleared the area is all well- 



wooded; the forest with its undergrowth is rich in species and tlic flora 



as a whole is strikingly dilTercnt from that of the bordering lowlands. 

 Amongst the characteristic trees and shrubs are the Scaly-bark Hickory, 

 Small-fruited Hickory {Carya glabra), Butternut (Juglans cinerca), Black 

 Wahmt (,/. nigra), Chin(piapin Oak {Qucrcus MuhlenhcTgii),Nov\\\cvnl{QCL 

 Oak {Q. borcalis var. ivaxima). Black Oak (Q. idutina), Schneck's Oak 

 (Q. SItumardii var ^chncckii), American and Red Elm (Uhnus amcricana, 

 U. fulva). Cucumber Tree (Magnolia acuminata), Tulip Treo, Sassafras, 

 Spice Bush (Benzoin acstivalc). Wild Cherry (Prunus srroiina). Red 

 Bud (Ccrcis canadensis). Sugar Maple (Acer saccharum and the variety 

 Schncckii), Linden (Tilia glabra). Sweet Gum, Black Gum, American 

 Ash, Tear Blanket (Aralia spinosa), and Wild Hydrangea. 



On the ui)]ands the trees often grow tall and straight and of a good 

 size for the resi)ectivc species; but the stand is .seldom so dense as in the 

 Cairo Formation, and the woods have an open park-like appearance, 

 with little undergrowth and few vines or herbs, except on steep hillsides 

 or in the protection of ravines and valleys. 



Just north of the town of Mounds, in Pulaski County, this flora and 

 the topography of the Cretaceous area that supjiorts it is typically de- 

 veloped; and from the mound-like character of the low hills, which lu 



ive 



presumably given the name to the town, the term Mounds Formation 

 seems quite ai>pr()priate for this floral province. However, while typic- 

 ally developed here, practically the same i)lant association is widely dis- 

 tributed beyond the Cretaceous area. 



Amongst the commonest undershrubs in the Mounds Formation arc 

 the Hazel, Si)ice Bush, Wild Black Raspberry and the smooth and ciner- 

 ous Hydrangeas (TI ydrangca arbor csccnsnudH. cinerca). Characteristic her- 

 baceous species are Phcgopfcris hcxagnnoptcra, Adiantum pcdatum, Dryop- 

 leris navcboraccnsis, Asplcnium fdix-fcmina, A. angustifolium, Carex 

 Jamcsii, Trillium grand ijlorum, Corallorrhiza Wistcriana, Aciaca rubra, 

 Aruncus Sylvester, Collinsonia canadensis, Eupatorium incarnatum and 

 Prcnanthcs (dfissim um. 



Several of the above species are found occasionally in the lowlands 

 of the Cairo Formation and the nuijority of them extend into the higher 

 rocky region to the north, but are comparatively rare or uncommon 

 there, while abundant and typical here. 



