566 W. M. DAVIS — DATES OF TOPOGRAPHIC FORMS. 



uplands (minus the altitude of its lowlands consequent on the late Tertiary 

 uplift, which, being of small amount, is not considered here) ; for while there 

 was certainly some faint slope toward the sea in the final lowland surface of 

 Cretaceous denudation, it must have been insignificant compared to the pres- 

 ent slope. The ease with which the rivers trench the plateau is alone suffi- 

 cient demonstration of this important fact. In northwestern Massachusetts 

 the topographic atlas of the state shows that the uplands reach an altitude 

 of 1,600 feet, and even 2,000 feet in the Taconic range on the western border 

 of the state. The New Jersey atlas shows that the inner or northwestern 

 division of the crystalline belt averages 800 or 1,000 feet along its front, de- 

 creasing toward the southwest. Along its northwestern margin, next to the 

 great valley, its height is from 1,200 to 1,300 feet. In Pennsylvania the 

 outer crystalline division at Philadelphia is 200 or 300 feet above tide. The 

 two parts of the inner division, both called South mountain in this state, are 

 elaborately mapped by the Second Geological Survey (see atlases to reports 

 D3, 1883, and D^, 1884) ; the one near the Delaware rises to 800 or 1,000 ; 

 the one between the Susquehanna and the Potomac reaches 1,800 or 2,000 

 feet. In Virginia, the Blue ridge, as the crystalline belt is there called, 

 ranges above 2,500, while its upland levels vary between 2,000 and 2,500, as 

 shown on the Luray, Roanoke and Dublin, Virginia, sheets of the United 

 States Geological Survey topographic maps.* In the southern part of 

 Virginia the detection of the peneplain in question is doubtful, but in North 

 Carolina it has been clearly recognized by Willis, who places his "Asheville 

 baselevel " at 2,400 feet elevation, while the piedmont belt on the eastern 

 side of the mountains, as described by Kerr, has an elevation of about 1,000 

 feet, gradually declining eastward. 



It must be remembered that in this part of the Atlantic slope the surface 

 was not by any means reduced to a flat lowdand in the Cretaceous cycle ; it 

 was a rugged country even at the close of Cretaceous time. In the broad 

 crystalline area of North Carolina, mountainous hills of from 3,000 to 4,000 

 feet rose above it, these being the mountains of that part of the Appalachians 

 to-day. Further on, in Georgia and Alabama, the ancient surface sinks 

 under the Cretaceous and new^er strata. 



Returning northward as far as New York, the inner part of the peneplain 

 may be examined. In the Catskills it is probably recognized at the eleva- 

 tion of the general upland surface, above which a series of moderate hills 

 rise to the highest summits and below which a number of narrow valleys are 

 cutting their way down to sea-level. Thus determined, it would stand about 

 2,500 feet above the sea ; the hills rise 500 feet or more higher yet. In 

 Kittatinny mountain, on the northwestern side of New Jersey, the crest-line 

 reaches 1,400 or 1,600 feet, and the plateau farther westward in northeastern 



* These maps will hereafter be referred to simply by the name of the sheet and state. 



