388 DAVIS — PLAINS OF MARINE AND SUBAERIAL DENUDATION. 



occupied in reducing; such inequalities as had been previously generated. During 

 periods of upheaval, and for a considerable time thereafter, the streams are cutting 

 down their channels, and weatiiering widens them into broad valleys with ridges 

 between. The diversification so produced reaches a maximum when tlie streams 

 have nearly reached their baselevels; but when tlie streams can no longer corrade, 

 and if the uplifting ceases, these diversifications are reduced and finally obliterated. 

 Such, I conceive, was the case here. . . . The entire region was planed down 

 to a comparatively smooth surface." * 



Willis first called attention to the occurrence of an uplifted and dis- 

 sected pene})lain of subaerial denudation in the mountains of North 

 Carolina,t and Hayes and Campbell have since then shown the" great 

 extent and area of this ancient hind surface. J Willis and Ha3^es have 

 lately described the northern and southern Aj)palachians,§ giving much 

 attention to the essential extinction of the mountains, except in tlie Caro- 

 lina highlands, in late Cretaceous time. The first author writes of tlie 

 lowland thus produced : " The land was flat, featureless and very slightly 

 elevated above the sea" (page 189). The second author writes : "The 

 whole region was reduced to a nearly featureless plain, relieved only by 

 a few groups of monadnocks where the highest mountains now stand " 

 (page 330). 



Emerson writes of the Berkshire hills in western Massachusetts: 



*' Erosion planed away the mountains to the general level, wdiich can still be seen 

 in the average level of the plateau, pitching slightly east. * * ^' When tiiis 

 peneplain was formed it was doubtless horizontid and near the sealevel, and was 

 what is called a baselevel." || 



Salisbury says that the even crest-lines of the New Jersey highlands 

 tell of " mountainous elevations reduced to a }>en('phiin near the level of 

 the sea."^i 



Not only the tilted rocks of tiie Alle^iieuies and of the older Ai)pa- 

 lacliian belt, but the horizontal strata of the Alleglieny plateau are 

 regarded as having been baseleveled, or almost so, before their present 

 ui)lift and dissection was gained. See, for example, the account of the 

 Cumberland plateau in Tennessee by Hayes.''"'' 



Griswold has recognized a greatly dissected })enei)lain in the even 

 crested ridges of the Arkansas novaculites, and has associated the warp, 

 ing of the great peneplain of whicli his special district was a ])art with the 

 origin of the lower course of the INIississippi in late Mesozoic timcff 



* Grand Canyon District. U. S. Geol. Survey Monogr., If, 188-2. p. 119. 



t Round about Asheviile, Nat. Geog. Magazine, vol. i, 1889, p. 297. 



I Geomorphology of the southern Appalachians, ibid., vol. vi, 1894, p. (j9. 



gNat. Geog. Monographs, vol. i, isgf), nos. G and 10. 



I Hawley sheet, Geo!. Atlas U. S., 1894. 



Ij Geol. Survey New Jersey, 1894 (1895), p. 8. 



**Sewanee siieet, Geol. Atlas U. S., 1895. 



ttGeol. Surv. Arkansas, 1890, vol. iii, p. 222; Proc. Bost. Soe, Nat. Hist., vol. xxvi, 1895, p. 478. 



