274 N. S. SHALEK — SPACING OF IIIVERS 



ditions of the country to the eastward. The Blue Ridge element of the 

 A[)i)alachian system is, as regards the liight of its peaks, even more irreg- 

 ular than the AUeghanies. While the last-named mountains exhibit a 

 general decline to the southward, varied by a few remaining high points, 

 the central ridge irregularly gains in altitude until the greatest hight is 

 attained, in the western part of North Carolina. Yet it must be assumed 

 that this portion of the Appalachian land was as much subjected to the 

 baseleveling actions as the Alleghany area could have been. Its rocks, 

 though harder, are more homogeneous than are the stratified beds on 

 the west, and are, moreover, of a nature more readily to yield to chem- 

 ical deca3^ Why, then, should baseleveling have been so effective in the 

 district less than 40 miles to the west and failed to take effect here ? 



The question just above asked again comes before us when we examine 

 the Piedmont area. We there find rocks in general character much like 

 those of the Blue Ridge, together with newer strata essentiall}^ of Triassic 

 ase, which have been folded and faulted down into them, have been worn 

 awa}'' until the mass forms a broad, rather uniform, field sloping gentlj'' 

 from the hight of about 1,000 feet to beneath the level of tlie sea. So 

 far as our knowledge of this and other continents goes, this area is in 

 aspect one of the most characteristically baseleveled areas that is known, 

 for in it an originally strong mountain topography, where rocks of ex- 

 ceedingly varied resistance are intimately commingled, have over a wide 

 field been reduced to a nearly uniform surface, having a gentle inclina- 

 tion seaward. It is true tliat here and there isolated peaks surpass this 

 plain, attaining to hights of several hundred feet above it; but although 

 these features have a value in tlie interpretation, they in nowise deprive 

 the district of its baseleveled character. Yet it appears impossible to 

 explain the level surface of this area on the hypothesis that it has been 

 worn down by river and atmospheric action. We can not apply this 

 explanation, for the reason that the plain passes abruptl}^ into the Blue 

 Ridge, which rises above it to a hight from a few hundred feet in tlie 

 Potomac valley to about 7,000 feet in North Carolina. It seems to me 

 questionable whether any form of the baseleveling hypothesis will alone 

 or even mainly account for this contrast in the character of the surface 

 of these level and mountainous areas. So far as I can see, the onl}' way 

 in which the facts can be reconciled -with that hypotbesis is b}^ the fur- 

 ther supposition that the Blue Ridge has been separated from the Pied- 

 mont area b^^relativel}' recent faulting which has lifted the mountainous 

 countr}' to its high level. It is necessar}'- to assume that this action took 

 place after the baseleveling of the seaboard district was efiectively ac- 

 complished. It is also to be noted that there is no evidence going to 



