The Peneplain. — Davis. 223 
the very region we had seen together. "How," I asked, "did 
you come upon that explanation?" "I cannot say precisely 
how," he replied; "it is nothing new." This incident seems to 
me to illustrate the unconscious encouragement given to the 
idea of peneplanation by a quiescent environment, in contrast 
to the discouragement given in such a region as the Alps. 
Unrest and quiescence are not persistent characteristics of 
one region or another. Pre-Cambrian time was active enough 
in the Wisconsin-Minnesota region ; and there are indications 
of relative quiet in the A.Ipine region before its ]\'Iesozoic and 
Cenozoic activity began. But this aspect of the problem is too 
large for consideration here. Suffice it to say that there is yet 
much to be learned about the past, and that I fully agree with 
McGee in believing that the world's history is to be read in 
denudation as v^ell as in deposition. If the deciphering of 
trustworthy records of denudation leads to the conclusion that 
the present is in some respects exceptional, a peculiar chapter 
in the earth's history, then I should have to add that conclu- 
sion to the other authenticated conclusion which go to making 
up the history of the planet. Admitting the present to be ex- 
ceptional in the lack of peneplains close to their baselevel of 
production, and thus postulating general disturbances by up- 
lift and tilting in the recent past, I doubt if this condition is 
more exceptional than that which permitted the widespread 
deposition of the chalk of Europe upon its even foundation, or 
than that which determined the formation of the Coal Meas- 
ures of Europe and North America. There does not seem to 
be any severe strain upon the reasonably elastic form of the 
doctrine of uniformitarianism in meeting the requirements of 
the peneplain theory. 
B 2. The earth's crust zvi/l not stand stiil lo/ii^ enougJi for 
the slozv process of deniidation to produce a peneplain. It is 
justly urged that according to theory the later stages of pene- 
planation are much longer than the early stages of dissection 
(p. 354), as Powell clearly pointed out some years ago; and 
it is inferred that the earth's crust will not stand still long 
enough for even penultimate denudation to be accomplished 
(p. 362). But the stability or instability of the earth's crust 
can be learned only by comparing the consequences reasonab- 
Iv deduced from one condition or the other with observed facts. 
