TIMES OF FORMATION OF TPIE PENEPLAINS O / / 



paper, however, he states* concerning the Cretaceous peneplain in New 

 Jersey : 



"The Seliooley peneplain is indicated by the crest and summit altitudes of 

 Kittatinny Mountain; ... its seaward portion descends slowly beneath a 

 cover of unconformable Cretaceous beds." 



If so, it nmst immediately antedate these Cretaceons beds. It should 

 be noted parenthetically that some physiographers^ have come to the con- 

 clusion that the Kittatinny and Schooley peneplains, are not the same, 

 in the same year Davis^ writes still more explicitly : 



"The date of the completion of tlie New Jersey peneplain ... is well 

 defined. . . . If the gently inclined peneplain be followed from the high- 

 lands towai'd the southeast, ... it is found to descend below the oldest 

 of the Cretaceous beds. . . . The weak Triassic formation . . . had been 

 baseleveled in Jurassic time." The highlands were then "worn down to a less 

 and less relief, and when the whole of Cretaceous time had elapsed the high- 

 lands must have reached the even surface now so conspicuous. . . . Erosion 

 of the surface may have continued into Tertiary time." 



Hayes and Camiobcll' say that 



"during Cretaceous time the condition of stability prevailed in this region for 

 the longest period of which we have any record in its history. . . . Through- 

 out this period of exceptional quiet erosion was in progress, reducing the sur- 

 face toward baselevel. The period of Tertiary baseleveling, on the other hand, 

 w\as comparatively short." 



Figures 1 and 3 of their discussion show a long period of erosion and 

 gradual reduction toward baselevel, "reaching from the final emergence 

 (Permian?) of the western half of the province to near the close of the 

 Cretaceous period,'' and a shorter cycle occupying a little more than half 

 the time since the opening of the Tertiary, followed by a still shorter 

 cycle extending to the present. 



Keith^ recognizes two Cretaceous, two Tertiary, and two Pleistocene 

 *^baselevels" in the region west of Washington, D. C. A portion of his 

 summary of tlie history of this region is as follows : 



11. Uplift, Newark deformation, and erosion to Catoctin baselevel. 



12. Depression and depositi(m of Potomjic, Mngothy, and Severn. 



* W. M. Davis: Itlvors of nortliern Now .Torsoy. Nal. Goos'. Mag., vol. 2, ISOO, p. SG. 



° G. W. Stose : Description of the Delaware Water Gap quadrauj^le, Delaware "Water 

 Gap, Pennsylvania-New Jersey. U. S. Geol. Survey, toi)ograpliic sheet, April, 1910. 

 . 8 W. M. Davis : The geologic dates of origin of certain topographic forms on the At- 

 lantic slope of the United States. Bull. Geol. Soc. Am., vol. 2, 1800, p. 554 et seq. 



7 Nat. Geog. Mag., vol. G, 181)4, pp. 69 and 84 and figs. 1 and 3. 



8 A. Keith : Geology of the Catoctin belt. U. S. Geol. Survey, Fourteenth Ann. Rept., 

 pt. 2, 1894, pp. 293-395. 



