248 THE PLANT LIFE OF MARYLAND 



tree. Here it is present in a considerable abundance in the forest, 

 and when open land is abandoned, it is an important tree in the 

 reforestation. 



Along the Ridge toward the north, or north-east, the conditions 

 continue much the same, occasional hog pockets in the sandstone 

 surface, with the plants already recorded in nearly constant variety. 

 Upon the upper portions of the ridge, in places having good soil 

 and considerable shade, the Paw Paw occurs in extensive clumps, 

 as it did in similar situations on Elk Ridge. 



In the drier woods the Corallorhiza multiflora is occasional and 

 Cypripedium acaule occurs in pine-needle soil. Scattered through 

 the forests Porteranthus trifoliatus, Medeola Virginia, Elephantopus 

 nudatus and Dioscorea villosa are rather common. 



Boulders. — The upper end of the Blue Ridge is of interest be- 

 cause of the presence in several places of "Rivers of Rocks" located 

 high above any present watercourse. These are collections of water 

 worn boulders, marking the bed of some ancient river, now aban- 

 doned through the cutting of new channels across the earlier chan- 

 nels. The ''river" may be several rods in width, and show no 

 evidence of water beyond the rounding of the boulders, and the 

 sound of a trickling stream at the bottom of the bed of rock, out 

 of sight below the lichen covered fragments. One such area is 

 located between Smithsburg and Wolfsville, in which the rocks are 

 not of great size. A more striking one is near Riven Rock, to the 

 south of Edgemont, in which the rocks are large, some of them 

 not fully rounded, but all worn by the action of the stream. 

 (Plate XXVL, Fig. 1.) 



The lichen covering of these rocks is largely of Umbilicaria, 

 which grows to the size of a disc six inches in diameter upon these 

 exposed rocks where there are few accidents to break the growing 

 thallus. Along with this Umbilicaria, there are of course the smaller 

 species, that are usually associated with the sandstone rocks, and 

 adhere closely to the rock surface. The general trend of the drain- 

 age which is represented by these channels, is toward the south- 

 east, while that of the present streams in the same area is south- 

 westward. 



