122 W. J. M c Gee — Three .Formations of 



Pennsylvania this mountain ridge looses its integrity and con- 

 tinuity and the boundary between the two zones is indefinite, 

 while in northern New Jersey and southern New York the 

 natural boundary fails and only an arbitrary demarkation can 

 be drawn between the zones so sharply distinguished in Vir- 

 ginia and Maryland. 



The Coastal plain extends from the line of cataracts and 

 crystalline rocks to the ocean. Structurally, it consists of 

 generally incoherent deposits of later Mesozoic and Cenozoic 

 age, slightly inclined seaward but otherwise undisturbed ; 

 topographically, it is a plain, trenched by broad but shallow 

 tidal estuaries and thus separable into smaller plains which 

 sometimes undulate gently but irregularly, and again take 

 the form of steeply-scarped terraces miles in extent, cut by 

 steep-sided ravines and deeply scalloped along the greater 

 waterways ; the hydrography comprises the broad flat-bottomed 

 estuaries into which the principal rivers are transformed on 

 entering the plain, and local drainage systems of widely branch- 

 ing dendritic type in which the principals are also generally 

 estuarine toward their mouths ; the divides are but labyrinth- 

 ine and crenulated remnants of an imperfectly drained plain 

 only partially invaded by erosion ; and throughout the region 

 the water is slack except toward the heads of the adolescent 

 drainage ways. The political boundaries and principal lines 

 of traffic are determined by the great water avenues, while the 

 civil boundaries and lesser lines of traffic are independent of 

 the physiography, and the industries grow out of the products 

 alike of sea and soil and out of the natural facilities for* traffic 

 and transportation. 



The common boundary of the Piedmont region and the 

 Coastal plain is one of the most strongly marked physiographic 

 and cultural lines on the land surface of the globe : On the 

 one hand there is a great series of crystalline rocks giving ori- 

 gin to a characteristic soil in which all streams, from the great- 

 est rivers to the smallest brooks, flow through constricted 

 gorges in a succession of cataracts or rapids ; while on the 

 other hand there is a series of incoherent and undisturbed de- 

 posits of clay, sand, and gravel through which the waters, 

 gathering in the more elevated zones, move sluggishly in broad 

 tidal estuaries. The boundary has long been known among 

 students of manufacturing industries as the fall-line ; yet it is 

 even more noteworthy as a line of deflection in the rivers 

 than as one of declivity. The great waterways of the Middle 

 Atlantic Slope maintain their courses through Appalachian 

 ranges and Piedmont highlands alike ; but on reaching the low- 

 lying Coastal plain they are turned aside, literally by a sand- 

 bank little higher than their depth, and thence hug the hard 



