14 JOURNAL OF THE ARNOLD ARBORETUM [vol. iv. 



dambar Styraciflua L., Primus mexicana Wats., Crataegus spathulata 



Michx., C. apiifolia Michx., Nyssa sylvaiica Marsh, and Fraxinus americana 



L. In the uplands as in the low woods the slight development of the lower 

 layerof shrubs and herbaceous plants is noticeable. Small patches or single 

 individuals of such minor trees and shrubs as Primus and Crataegus, Ilex 

 decidua Walt., Vaccinium arbor eum Marsh., Rubus Andrew si anus Blanch., 

 Rhus copallina L. and Rosa setigera Michx. are sometimes found along 

 the borders or in the more open portions. Grasses and herbaceous 

 flowering plants are generally almost entirely absent. In a few larger 

 openings, on the banks of streams and along the escarpment many otl 

 species appear and something like thickets with a tangle of shrubs and 

 vines is developed. In such places grow several additional species of 



Crataegus of the Crus-galli, Virides and Punctalae groups, Mai us ioensis 

 var. Palmeri Relid., Zanthoxylum Clava-Herculis L., Cercis canadensis 

 L., Diospyros virginiana L., Bumelia lanuginosa Pers., Smilax bona-nox 

 L., Berchemia scandens Trel. and A tnpelopsis arborea Koehne. Many kinds 

 of non-woody flowering plants also manage to thrive here. Where the 

 clay and gravel are much eroded, as is sometimes the case on steepish 

 hillsides, a somewhat more xerophytic phase of the flora is developed. 

 Juniperus virginiana L., Madura pomifera Schneid., Berchemia scandens 

 Trel. and Cocculus carol in us DC. seem at home here, and some of the 

 herbaceous species are even more characteristic, such as Ophioglossum 

 Engelmanni Prantl, Agave virgin ica L. and Opuntia humifusa Raf. 



Where the Lafayette gravel and clay is absent and the Cretaceous form- 

 ations appear on the surface, conditions are very different. The soil is 

 of a loose sandy loam, often quite fertile on account of the shell-marl and 

 humus which it contains. The surface is easily eroded and often deep 

 gullies and canyons are found working back into the plateau. Perennial 

 springs issue in some of these hollows, and their banks are clothed with 

 many species of ferns, flowers and shrubs. Sometimes remnants of the 

 gravel and clay cap the domes or ridges between the ravines, and there is a 

 descending scale of sterile gravelly flat, sandy slopes, deep protected banks 

 and lower dow r n perhaps a sandy bog bordering a stream or bayou. It is 

 in such situations that the peculiarly rich flora has developed and many of 

 the rare plants are found. A short distance southwest of the railway 

 station at the village of McNab, near the junction of Yellow Creek and 

 Little River, these conditions are typically developed. A deep cut in the 

 railway grade gives an excellent exposure of part of the geologic section. 

 Layers of soft sandstone from one to two meters thick, carrying many 

 large calcareous oyster shells and other fossils, were seen with five 

 or six meters of fine unconsolidated sand above and a similar deposit 

 beneath. Near the point where the railroad crosses Little River the 

 valley is bounded by a bluff, the highest and most precipilous to be found 

 in the vicinity. At the highest point it rises perhaps 18 to 20 meters above 

 the valley, and as it has a northern exposure and a slope of from 60 to 75 



