BASELEVEL, GRADE AND PENEPLAIN 87 
that the river has to do. The changes continue until the two 
quantities, at first unequal, reach equality; and then the river 
may be said to be graded, or to have reached the condition of 
grade. This condition cannot be understood without rather 
careful thinking on the part of the expert as well as of the tyro. 
The idea of grade is not of almost axiomatic simplicity, like 
the idea of baselevel; its meaning must be gradually elaborated 
as it is approached. Moreover, a graded river does not main- 
tain a constant slope; it changes its slope systematically with 
the progress of the cycle: but before taking up this element of 
the discussion a few paragraphs may be given to the considera- 
d 
tion of ‘‘grade,’’ as a common word used in a technical sense. 
It should be noted in the first place that it is a condition of 
river development, not a surface, nor a stage, nor a form, for 
which the term ‘“‘grade”’ is to serve as a name. The condition 
of grade must not be confused with the limiting under-surface 
of erosion, with respect to which the graded condition is devel- 
oped; the name for this surface is ‘‘baselevel.’’ Nor must it be 
confused with the stage in the history of river development in 
which the graded condition is reached ; ‘“‘maturity’ 
for that stage; but it may be noted in passing that the graded 
condition persists all through the old age as well as the maturity 
of an uninterrupted cycle. ‘‘Grade,’’ meaning a condition or 
, 
is the name 
balance, must not be confused with the same word used in 
another meaning, namely, the slope or declivity of the river when 
the graded condition is reached; for ‘‘grade”’ meaning slope, 
varies in place and in time, while ‘‘grade,’’ meaning balance, 
always implies an equality of two quantities. In fine, grade is 
a condition of essential balance between corrasion and deposi- 
tion, usually reached by rivers in the mature stage of their 
development, when their slopes have been duly worn down or 
built up with respect to the baselevel of their basin. 
There can be no question that the balanced condition of 
mature and old rivers deserves a name. It was to this condi- 
tion that Powell called attention in his original discussion of 
land sculpture, and to which he devoted one of the meanings of 
