128 THE AMERICAN NATURALIST. (VoL. XXXIII. 
that continental oscillations of level are too pronounced, both 
from the point of view of amplitude and of frequency, to allow 
of the amount of beveling requisite to reduce a mountain-built 
region to the faint relief of a peneplain. (3) There is no 
known case of a modern extensive peneplain standing at its 
baselevel. (4) The paper is, however, largely occupied with 
a concrete argument against the peneplain from an analysis of 
the facts of land-form in two of the classic regions where the 
peneplain was first described, namely, in New England and New 
Jersey. 
Before proceeding to a detailed discussion of these various 
points it is necessary to observe that, in order adequately to 
demolish the theory, it must be inspected, not only in the writ- 
ings of the American physiographers, but also in those of Euro- 
pean authorship. The peneplain is an American idea, but it 
has taken firm root in Europe. Men like Penck, Philippson, De 
Margerie, and De Lapparent are recognizing its truth, and we 
read of the peneplains of Bohemia, Russia, and the Rhine dis- 
trict; yet we cannot say that these men are specially omniv- 
orous of American geological and geographical conclusions. 
We may most heartily agree with Professor Tarr in his calling 
a halt on the wholesale discovery of peneplains on insufficient 
evidence, but that criticism does not apply to the examples 
cited. 
1. Professor Tarr refers to the difficulty of finding time 
enough for the process of the peneplanation of a mountainous 
tract, from the fact that, since the glacial period, there has been 
sufficient time neither to “strip off the till left by the ice upon 
the hillsides [of New England], nor to notably modify the very 
perfect form of drumlins, eskers, and deltas formed when the 
ice was here.” ‘When we see the slowness of denudation in 
a hilly country, even a single peneplain seems most difficult to 
conceive.” Is it easier to conceive (i.e. actually measure out 
in the imagination) a stretch of time long enough even to per- 
mit of the excavation of the Colorado Canyon or the retreat of 
the Niagara escarpment fifty miles or more from the former 
edge of the Niagara limestone, or to produce the bewildering 
network of valleys in the West Virginia plateau? Whether we 
