TOPOGRAPHIC FEATURES. 325 



The escarpment throughout the area described is determined in part 

 by the character of the Upper Cretaceous strata and in part by under- 

 lying and overlying formations. The great difference in the volume of 

 the Upper Cretaceous deposits in passing from the northern to the south- 

 ern portions of the district is very marked, and the strata become a con- 

 stantly less important factor in determining the topography. 



The escarpment faces the more readily eroded deposits of the Lower 

 Cretaceous, and, throughout the larger portion of New Jersey, the lowest 

 member of the Upper Cretaceous series as well. This formation, how- 

 ever, rises also into the base of the escarpment, although the escarpment 

 proper is made up of the higher members of the series and the forma- 

 tions which overlie them. As these upper members gradually disappear 

 to the southward the Tertiary becomes a more and more prominent 

 factor in the formation of the escarpment, which in Maryland is largely 

 to be accounted for upon these grounds. In no portion of Maryland, not 

 even upon the western shore, where the country is much higher than 

 upon the eastern shore of the Chesapeake, are there elevations in any 

 way comparable with those found in northern New Jersey ; yet the edge 

 of the escarpment, especially to the south of the Severn river, frequently 

 reaches a height of 200 feet, and does not fall much below that elevation 

 even in the valley of the Potomac river. 



The streams show a marked difference in their valley characters, de- 

 pendent on whether they drain directly to the Atlantic by easterly and 

 southerly courses, or whether they flow to the west toward the fall-line. 

 The valleys of the Atlantic drainage are broad, the land rising gently on 

 either bank, while the channels of the streams flowing toward the fall-line 

 have much steeper slopes and are generally U-shaped. An explanation 

 for this may be found in the stratigraphy of the region, since the strata 

 dip slightly to the southeastward, so that the streams flowing in that di- 

 rection follow the slope of the beds, while those flowing to the northward 

 must cut across their upturned edges. As the beds vary in hardness 

 the widening of the channel must be retarded by the hardest layers. 



Description of the Formations. 



general statement. 



The geological formations of the Coastal area of New Jersey, Delaware, 

 and Maryland represent a nearly complete sequence from the base of the 

 Cretaceous to the Pleistocene. They form a series of thin sheets which 

 are inclined slightly to the southeastward, so that successively later forma- 

 tions are encountered in crossing the district in that direction. Variation^ 

 in the angle and direction of tilting and later denudation have occasioned 



