CONTINENTAL SHELF. 43 



Another reason for the disappearance of the topographical relief of the 

 East Appalachians can be found in the marine erosion to which the}' have 

 been subjected. As before remarked, it is evident that the Atlantic coast of 

 this continent has for a very long time been in about its present relations 

 to the sea. It is characteristically an old shore, and has the marks of age 

 in the broad continental shelf which fringes it on the east and in the wide 

 belt of lowlands which lies to the landward of the coast line. These two 

 features seem to be closely related to each other; the submarine shelf 

 probably represents in good part the accumulations of debris which has 

 been worn from the bench which the sea has cut into the land. 



Because it is covered by the sea, we can determine but little of the 

 continental shelf, except by inference from what we reasonably take to be 

 an emerged part of its mass as it appears in the structure of the great 

 southern coastal plain, that plain land being evidently composed of conti- 

 nental waste in part removed by marine action, together with the de'bris of 

 organic forms; but of the bench we may know much, for the greater part 

 of it is above the sea level. If the student would appreciate the importance 

 of this seaboard bench on the Atlantic coast of the United States, he should 

 study the section from the great Appalachian Valley to the sea. Probably 

 the most instructive section is from the region of the upper Shenandoah to 

 the region about Fort Monroe, in Virginia. It is readily noted that the 

 crystalline rocks on the western side of the Blue Ridge rise steeply 

 from the broad vale which is occupied by the Cambrian beds. On this 

 side of the ridge there is no trace of benching; the mountain sides show the 

 ordinary torrent slopes. On the eastern side of the ridge, however, there 

 lies the extensive rolling country commonly known as the " Piedmont 

 Plateau," which has been recognized as a peculiar feature in the section 

 from New Jersey to Georgia ever since the country was occupied by the 

 Europeans. This region has peculiarities of soil and of surface aspect 

 which are due to the fact that it is to a great extent underlain by crystalline 

 or metamorphosed rocks essentiallv like the complex which makes the 

 higher country of the Blue Ridge. When the rocks exhibit bedding, the 

 attitudes of the strata indicate highly compressed mountain folds. The 

 topography of the district shows much torrent cutting on the surface of a 

 sloping bench which declined toward the sea at the rate of 10 or 20 feet 

 to the mile, the upper or northern margin of this bench passing rather 

 suddenly into the steep slopes of the mountain ranges. 



