\ 
Tlie Peneplain. — Davis. 213 
the existing ridges were the unconsumed remnants of the an- 
cient Appalachians, and by imphcation, that no upHft of the 
region had occurred since the mountains were crushed, folde*^ 
and upheaved. So in southern New England: there was no 
means of determining the date of uplift, as a result of which 
the existing valleys were eroded, until the peneplain of the 
uplands was recognized and dated. Twenty or thirty years 
ago, it was not uncommon to meet the suggestion that the 
valleys might be of glacial origin, so little understanding 
had then been reached of the geographical development of the 
region. Those who believe in the verity of peneplains will 
infer uplift, where they see a high-standing and dissected 
peneplain, as confidently as the geologists of the end of the 
eighteenth century inferred uplift when they found marine 
fossils in stratified rocks far above sea level. 
But it does not seem warranted to conclude that the pene- 
plain theory is invalidated because certain peneplains are now 
uplifted on a slant, although this is implied in Professor Tarr's 
argument (p. 359). It is no objection to the peneplain idea ' 
to say that the crest of Kittatinny mountain is higher than 
the upland surface of the New Jersey highlands (p. 356), or 
that the crest of the palisades is lower. It would be as ex- 
traordinary to find no slanting peneplains as to find no in- 
clined strata. Warped and faulted peneplains are no more 
unlikely products of crust al deformation than warped and 
faulted sedimentary formations ; witness the dislocations of the 
plateaus trenched by the Colorado canyon, the plateau surface 
having been worn down .to "a very flat expanse" before the 
uplift and displacements that have determined the altitudes 
and forms of to-day. 
A 5. Objections based on the fragmentary condition of 
certain peneplains further considered. If the best preserved 
peneplains were not less fragmentary than the ones that Pro- 
fessor Tarr has discussed quantitatively, the theory of pene- 
plains'might perhaps be overthrown: but when the imperfect 
])eneplains of N^ew England and New Jersey are considered 
in connection with many more nearly perfect peneplains else- 
where, the series becomes so well graded, from better to 
worse, that the theory seems to me unassailable. A few ex- 
amples of the better preserved peneplains may therefore bo 
now considered. 
