222 National Geographic Magazine. 



chief consideration in onr problem. When we remember how 

 accurately water finds its level, it will be clearer that what is 

 needed in the discussion is the location of the regions that were 

 relatively raised and lowered, as we shall then have marked out 

 the general course of the consequent water ways and the trend of 

 the intervening constructional ridges. 



Accepting these postulates, it may be said in brief that the 

 outlines of the formations as at present exposed are in effect So 

 many contour lines of the old constructional surface, on which 

 the Permian rivers took their consequent courses. Where the 

 Trenton limestone is now seen, the greatest amount of overlying 

 strata must have been removed ; hence the outline of the Trenton 

 formation is our highest contour line. Where the Helderberg 

 limestone appears, there has been a less amount of material 

 removed ; hence the Helderberg outcrop is a contour of less 

 elevation. Where the coal beds still are preserved, there has 

 been least wasting, and these beds therefore mark the lowest 

 contour of the early surface. It is manifest that this method 

 assumes that the present outci'ops are on a level surface ; this is 

 not true, for the ridges through the State rise a thousand feet 

 more or less over the intervening valley lowlands, and yet the 

 existing relief does not count for much in discussing the enormous 

 relief of the Permian surface that must have been measured in 

 tens of thousands of feet at the time of its greatest strength. 



25. Constructional Permian topography and consequent drain- 

 age. — A rough restoration of the early constructional topography 

 is given in fig. 21 for the central part of the State, the closest 

 shading being the area of the Trenton limestone, indicating the 

 highest ground, or better, the places of greatest elevation, while 

 the Carboniferous area is unshaded, indicating the early lowlands. 

 The prevalence of northeast and southwest trends was then even 

 more pronounced than now. Several of the stronger elements of 

 form deserve names, for convenient reference. Thus we have 

 the great Kittatinny or Cumberland highland, C, C, on the south- 

 east, backed by the older mountains of Cambrian and Archean 

 rocks, falling by the Kittatinny slope to the synclinal lowland 

 troughs of the central district. In this lower ground lay the 

 synclinal troughs of the eastern coal regions, and the more local 

 Broad Top basin, BT, on the southwest, then better than now 

 deserving the name of basins. Beyond the corrugated area that 

 connected the coal basins rose the great Mttany highland, N, 



