292 THE PLANT LIFE OF MARYLAND 



plays a more important role in determining the vegetation, being 

 responsible for the distinctions of Ridge, Slope, Glade and Swamp. 

 The character of the Ridges will not be lost until they are worn well 

 down toward the level of the Valleys, when they will pass through 

 the slope stage to that of the Valleys, when, for the first time in their 

 history, the influence of the subjacent rock will be manifested, sand- 

 stone soil supporting the Sand type and shale soil the Loam type. 

 The weathering of the Rocky Slopes and the carrying of erosion 

 materials down onto them will make them approach the soil-covered 

 Slopes in character. The silting up of the Swamps will lead to the 

 invasion of them by Glade forest, which may be in turn invaded 

 by the Valley type, although little evidence of such invasion has 

 been observed. 



