124 HARRY N. EATON 



the Tuscarora summits south of Potters Mills and Boalsburg: 

 Broad Mountain, 2,300 feet; Millikens Knob, 2,200 feet; a crest 

 two miles south of Boalsburg, 2,300 feet; the mountain on road 

 south of Pine Grove Mills, 2,010 feet; Roberts Knob, 2,410 feet; 

 and Bear Meadows Mountain, 2,100 to 2,200 feet. The same map 

 gives the following readings for the Oswego ridge summits: a ridge 

 running from Bear Meadows north of Roberts Knob 26 miles 

 northeast to Woodward, 1,700 feet average, attaining 1,800 feet 

 in a few places; a corresponding ridge one mile southeast of the 

 preceding on the other limb of the syncline, averages i ,800 feet for 

 many miles; Tussey Knob, east of Boalsburg, rises to an altitude of 

 2,100 feet, rapidly sinking to the southwest to 1,600 and 1,700 feet 

 average. 



Making allowance for possible slight inaccuracies in these map 

 elevations a distinct discordance in height between the summits 

 of the Oswego and Tuscarora ridges, in general, becomes manifest 

 from the foregoing data. This discordance may be observed in the 

 field, either from one of the higher and more commanding points 

 on the Nittany valley lowland, or from some coign of vantage in 

 the Seven Mountains, such as Roberts Knob. After six years' 

 residence in the Nittany valley the writer is convinced that this 

 difference in summit levels in the central Pennsylvania district 

 is an important factor which cannot be passed over with the facihty 

 of some previous writers. 



Space does not permit here the enumeration of instances of the 

 difference in heights of adjacent mountain ridges in other states, 

 but one example will show how universal the phenomenon is. In 

 the Hancock, Maryland-West Virginia-Pennsylvania quadrangle 

 the Cretaceous peneplain has been obliterated entirely in all 

 probabihty, according to Stose,' but is preserved in the 2,000- to 

 2,200-foot summit of Cacapon Mountain in the Pawpaw quad- 

 rangle. This author^ distinguishes between the Somerville (New 

 Jersey peneplain) terrace^ varying from 600 to 850 feet in elevation, 



' G. W. Stose and C. K. Swartz, "Pawpaw-Hancock Folio, Md.-W. Va.-Pa.," 

 U.S. Geol. Surv., No. 179 (191 2), pp. 19-20. 

 ^ Ibid., p. 20. 

 ^ 3 Davis and Wood, op. cit., pp. 391-92. 



