150 THE PLAETT I.IKE OF MARYLAND 



of a right-angled triangle with the apex in western Charles County 

 and the hypotenuse along Chesapeake Bay. Along its western side, 

 where it does not border on the Potomac Eiver it merges into the 

 Piedmont Plateau, or Midland Zone. The total area is about 2100 

 square miles. Except along the shore of Calvert County, the coast 

 is much indented by estuaries. As to relief the surface may be 

 roughly divided into (1) a bordering fringe of low flat country 

 having a greater or less breadth and occupying the bulk of the 

 peninsulas such as Gunpowder Neck, and (2) an inner plateau 

 ranging in height from 120 to 250 feet or more, where it joins 

 the Midland Zone. The second section is usually gently undulating, 

 but in some places the divides are scored by deep ravines, as in 

 the vicinity of Marlborough, Prince George's County. On the east 

 side of Calvert County the marginal strip is lacking, and the shore 

 is precipitous owing to the erosion along the western side of Ches- 

 apeake Bay. In most instances a narrow strip of sandy beach lines 

 the cliff, but on headlands the sediment has been swept away by 

 littoral currents. For a more detailed account of the topography 

 of the region the reader is referred to Vol. I. of the Publications 

 of the Maryland Weather Service. 



Owing to the labors of the Soil Survey, the soils of the region are 

 well understood, the following counties having been surveyed: St. 

 Mary's, Calvert, Prince George's and Harford. The results so 

 obtained have been used as a basis for many of the observations made 

 in the present chapter. Throughout the Coastal Plain only sedi- 

 mentary deposits occur, consisting of unconsolidated sands, clays 

 and gravels, together with remains of organic life such as marl beds. 

 In most parts of the area the bed-rock lies too far below the sur- 

 face to exert any influence on vegetation. The soils represent de- 

 posits of material of a variety of kinds brought by streams and 

 littoral currents during one or another of the periods of submer- 

 gence of the region. These deposits have been repeatedly elevated 

 and subjected to the action of atmospheric agents and running 

 water, so that the materials have undergone some rearrangement 

 even since the last elevation of the strata. The effect of this series 

 of events has been to mix the deposits which may earlier have been 



