The Peneplain. — Davis. 221 
cates of the explanation." I am no more willing to be consid- 
ered an advocate than I suppose Professor Tarr is to be 
thought an enemy of peneplanation. We are not retained to 
argue for or against the theory ; each of us follows the guid- 
ance of the best evidence he can find. I trust that Professor 
Tarr is just as much interested to discover whether monad- 
nock rocks are resistant as I am to discover whether his theory 
will account for uplands with even skylines. It is of course 
difficult to avoid the appearance and even the style of the ad- 
vocate or the enemy when writing earnestly in expression of 
one's convictions, but for my part I cannot say too emphatically 
that the peneplain idea shall find no "defense"' from me. Let 
us all set forth the/r6'.y and co)is to the best of our ability, and 
then the peneplain idea must look out for itself, and stand or 
fall according to its value. 
The objections thus far discussed relate to actual examples 
of supposed peneplains. Attention may be next turned to a 
group of objections based on general considerations, leadiiig 
to the belief that the production or occurrence of peneplains 
is improbable or even impossible. 
B. I. No peneplains are noiv found standing close to base- 
level. It is stated that "710 extensive peneplains [not uplifted 
or dissected] are known to exist at the present time in any 
part of the earth," although "peneplains have been jiroduced 
again and again in the past. * * * Therefore, in accept- 
ing the peneplain theory, we need, as a fundamental assunui- 
tion, to believe that during a part of the remote past, the 
conditions have been different from these that have prevailed 
in any part of the known earth during the present and im- 
mediate past" (p. 353, 354). Here Professor Tarr and I are in 
essential accord, although I should prefer to replace "funda- 
mental assumption" by "necessary corollary." As far as my 
own understanding of the problem is concerned, it was not at 
all as a fimdamental assumption, but as a very surprising cor- 
ollary that I came upon the difference between the present and 
certain parts of the past, with respect to ])eneplanation. This 
aspect of the question has often been discussed with my ad- 
vanced classes, but it has not yet received the attention that it 
deserves, and I am obliged to Professor Tarr for bringing it 
clearlv forward. 
