108 STUDIES FOR SFUDENTS 
words to the facts as convenient handles by which to bring the 
facts forward. It is a fact of large import that the wearing 
down of land masses proceeds in an orderly manner, involving 
the disclosure of bare rock ledges (denudation) in the earlier 
stages of the cycle of erosion, and the concealment of all ledges 
under a graded sheet of waste in the later stages of the cycle 
(degradation). It is a fact of much delicacy that streams tend 
to assume a balanced condition as to corrasion and transporta- 
tion; that after once attaining this condition they preserve it as 
long as their work continues without disturbance; but that the 
slope of their graded courses must vary systematically through 
the stages of maturity and old age, as well as through changes 
of climate. It is a fact of great value in geographical descrip- 
tion that the balanced condition of water streams is imitated so 
closely by that of waste streams that one set of terms applies to 
both kinds of streams. 
There can be no question that the adoption of a suitable 
term as the name for a fact is a great aid to the general recog- 
nition of the fact itself. It is largely on this account, as well as 
in the interests of a precise terminology, that I have here writ- 
ten out a series of notes that have been gathered during the 
past two years, and of which some account was given at the 
meeting of the Geological Society of America in Washington, 
in December, 1899. 
It is admittedly difficult always to use terms in a manner 
that is perfectly consistent with their definitions. It is rarely 
possible to limit terms to a single meaning. It is probable that 
in this attempt to reduce our terminology to greater simplicity 
and better order than now prevails I have laid myself open to 
criticism on the very grounds that are objected to in the course 
of this essay. Further discussion may therefore be advisedly 
directed to a settlement of open questions. It is certainly open to 
consideration whether ‘‘denudation”’ and “ degradation ’’ should 
be limited as above suggested ; but the advisability of holding 
‘“‘baselevel” and ‘‘ grade” to the meanings here indicated seems 
to me much less open to difference of opinion. The future 
