354 TJie American Geologist. -,1898 
have been periods of sufficient land rest to allow mountain 
masses to be worn down to very near the base level. This 
means relative quiet, or fluctuations about an average level, 
for a sufficiently long period of time to admit of the slow 
process of approximate base leveling. Therefore, in accept- 
ing the peneplain theory, we need, as a fundamental assump- 
tion, to believe that during a part of the remote past, the con- 
ditions have been different from those that have prevailed in 
any portion of the known earth during the present and imme- 
diate past. 
Few American geologists will be found who will deny the 
possibility of base leveling, — that, given time, the surface of 
the land will be leveled to the condition of a peneplain. Such 
a principle may readily be given a place in an ideal cycle of 
land development but there should be some real evidence 
before applying the ideal to the interpretation of existing con- 
ditions. 
The wearing down of elevated mountains to those of mod- 
erate relief may be granted, and the theoretical possibility of 
their further reduction to the base level may also be accepted. 
But when the stage of maturity has been reached, the further 
process of down-wearing must become progressively slower. 
This will be so, partly because decreased relief of land dimin- 
ishes the power of the agents of denudation, and partly in 
a more indirect manner, by furnishing to the imdulating sur- 
face a capping of residual soil which protects the rock from 
the action of many of the agents of weathering. It seems 
impossible to state just what would be the curve of rapidity 
of denudation with diminishing altitude, but it is evident that 
the rate diminishes so rapidly with decreasing slope, that, 
before the condition of the peneplain is really reached, the 
rate of down wearing must become exceedingly slow. 
In the summer of 1897 I spent a month among the moun- 
tains of central Maine, the larger part of the time being in the 
Penobscot drainage area. When I started upon the ascent of 
Mt. Katahdin, there had been five days of very heavy rain, 
so that the mountain trails were transformed to brooks, and 
the East Branch of the Penobscot had risen a number of feet, 
almost to the level of the spring freshets. The trail up the 
mountain led across this river, which was fed bv mountain 
