Davis and Wood.] 
386 
Nov. 20, 
scribed under the name of the Schooley baselevel peneplain. This 
peneplain, with the unconformable cover of Cretaceous beds that 
subsequently transgressed over its eastern margin, was at some 
later time elevated in the interior, and in the declining surface of 
the plateau thus formed the valleys of the Highlands and the low- 
lands of the softer Triassic beds have been cut out, at times and to 
an amount that will be considered farther on. The Appalachian 
chain, as we now see it, is therefore not to be regarded as the re- 
sidual relief of an elevation given once for all at the time of the 
great Permian folding. The first and probably the greatest Ap- 
palachians were worn down low before and during Triassic time ; 
they were regenerated to a considerable strength by the post-Triassic 
faulting, tilting and elevation, and again worn down low and faint 
to the Schooley baselevel peneplain ; and the ridges that we now 
see are simply the parts of this old peneplain that have as yet with- 
stood the erosion consequent on a still later uplift. The first ele- 
vation was accompanied by tremendous crushing and folding ; the 
second was accompanied by little more than monoclinal tilting and 
faulting ; the third, as well as other minor oscillations of later date, 
were chiefly massive uplifts of moderate amount and gentle ine- 
quality. 1 
It appears then that the period of the Schooley baselevel was of 
later date than the post-Triassic tilting, that it was of earlier date 
than the oldest of the strata that lie upon it in the New Brunswick 
district, and according to recent determinations these are of low 
Cretaceous or perhaps late Jurassic time. From this it may be con- 
cluded that the Schooley baselevel attitude was taken and main- 
tained during Jurassic time ; and that the baselevelling of the older 
Highland mountains into the old Highland peneplain was well ad- 
vanced in the same period. 
19. Character of deposits overlying the Schooley peneplain. The 
southeastward extension of the Schooley peneplain may be followed 
beneath the unconformably overlying Cretaceous beds ; 2 and from 
this we must conclude that at least this portion of'the plain suffered 
some depression after its baselevelling and before its elevation to 
its present altitude. This forms a subdivision of the Schooley cy- 
cle. The depression occurred after the deep denudation of the 
Triassic shaly area, for the northwestern margin of the overlying 
1 Compare Willis, Nat. Geogr. Mag., 1, 1889, 299. 
2 McGee’s Potomac formation is here included with the Cretaceous. 
