The Peneplain. — Tarr. 361 
the fact that the region is a lowered mountain mass, evi- 
dently once of very rugged topography, but now much re- 
duced and traversed by drainage lines of a somewhat mature 
form, the result of elevation. These facts I accept; but I be- 
lieve that they admit of a much simpler explanation, which is 
proposed in a later part of the paper where this point can 
be considered more appropriately than here. 
Evidence Against the Peneplai7i Tlieory. — It is difficult 
to find positive evidence against this explanation. In fact it 
would seeni hardly necessary to do so, since the burden of 
proof should rest with the advocates of the explanation. At 
present it is generally accepted, not as a theory to be consid- 
ered possible, but as a fact amply proved and to be accepted 
without question. Convincing evidence in its favor, which 
would place it upon a more solid foundation than that of a 
mere theory, I am unable to find, though I have searched care- 
fully for it. I should like to have a statement of the evidence 
which gives the explanation any other rank than that of a 
hypothesis. 
The point already dwelt upon concerning the improbability 
of the explanation seems to bear evidence against the pene- 
plain. The length of tinje required to reduce a surface to thisf 
condition, and the necessity of assuming a moderate uniform-! 
ity of level, or an oscillation about an average level during all] 
this time, argues against the explanation. The time since 
the glacial period, by many believed to be represented in from 
5,000 to 10,000 years, though lately multiplied several times 
this by some, has not been sufficient to strip ofif the till left 
by the ice upon the hillsides, nor to notably modify the very 
perfect form of drumlins, eskers and deltas formed when the 
ice w^as here. Yet mountains have been reduced to the condi- 
tion of a plain so uniform that, from the remnants left us, one 
has but to climb to the hilltop to see the proof of a plain, need- 
ing only a power of imagination sufficient to fill up the valleys 
between the hills and thus build up the former undulating sur- 
face. When we see the slowness of denudation in a hilly 
country even a single peneplain seems most difficult to con- 
ceive; but when three, four, or even five successive peneplains 
are argued, as if it were as natural to grind down mountains to 
form plains as it would be to clip of¥ the edges of these pages, 
