The Peneplain. — Davis. 209 
ture very generally indicates a belief in plains of marine abra- 
sion, a number of geologists have, without public announce- 
ment in any formal manner, gradually enlarged the share of 
work attributed to subaerial forces, until, as some of them 
have lately assured me, the "peneplain idea" has come to be 
for a number of years as familiar to them as to most Ameri- 
can geologists; and some of them certainly entertained it be- 
fore the term, peneplain, was suggested. Several examples 
of therecognition of the "peneplain idea" by continental geolo- 
gists might be given if time and space permitted, but I will 
here refer only to the essay by Penck, quoted below (B 4). 
Professor Tarr argues, in effect, that certain regions in- 
stanced as dissected peneplains have never really been low- 
lands of faint relief; that the process of peneplanation is in 
itself an extremely vmlikely one; and that the so-called pene- 
plains, all of which are now more or less dissected, are cap- 
able of other explanation; in brief, that peneplains are (A) 
luireal, (B) improbable, and (C) unnecessary. Several sub- 
divisions of each of these headings will be made in replying 
to them. Page numbers refer to Professor Tarr's original 
article. 
A I. Certain regions slicnv no trace of peneplanation. It 
is stated that "one standing upon the crest of one* of the 
mountains of central Maine would hardly find the evenness 
[of the sky line] sufficient to give the appearance of levelness 
even to the eye" (p. 357). But no one, so far as I know, has 
thought that the mountain tops of Maine mark the remnants 
of a peneplain. The mountains there are probablv of the 
nature of monadnocks; it is only the general upland surface 
above which the mountains rise that can be regarded as a 
peneplain, uplifted and dissected, if the features that I have 
seen about Portland and at some other points along the coast 
may be extended inland. The White mountains have been, 
in my mind, tentatively classed as a group of monadnocks; 
they do not, as far as I have seen them in brief excursions, 
stand upon any distinct basement comparable to that of the 
uplands of New England further south; but Mr. Philip Em- 
erson, master of the Cobbett school, Lynn, tells me that he 
has in summer excursions traced what he thinks mav be re- 
garded as the extension of the more southern uplands around 
