102 STUDIES FOR STUDENTS 
headward growth of the graded slope next below it, just as 
every ledge of rocks that makes a fall or rapid at the head 
of a reach will, in time, be obliterated by the up-stream exten- 
sion of the graded reach. (In both cases, when the time of 
extinction of the ledge is attained, the waste slope and the 
stream reach will probably have been worn somewhat farther 
into the land-mass, assuming a somewhat fainter declivity— 
that is, coming closer to baselevel—than was the case while 
the ledge still existed.) 
The close similarity, the real homology between the two 
classes of streams, makes it all the clearer that ‘‘ baselevel”’ 
is not a good term to apply to either. It is not desirable to 
say that a hillside ledge is ‘‘baseleveled” when it is worn 
back so far that it disappears under the slope of the grow- 
ing sheet of waste; yet it is certainly desirable to indicate 
by the use of an appropriate terminology that the disap- 
pearance of the ledge has been accomplished by changes of 
the same kind as those which have caused the obliteration 
of falls and rapids in rivers. Hence it seems desirable to 
say that every ledge, in valley side or stream bed, will in 
time be graded—not baseleveled—with respect to the atti- 
tude assumed at that future time by the graded—not baseleveled 
—reach or slope next below it. 
It is, perhaps, on account of the elusive character of 
the imaginary warped surface that its definition is sometimes 
couched in indefinite language. In the original definition, 
Powell said: 
I take some liberty in using the term level in this connection, as the action 
of a stream in wearing its channel ceases, for all practical purposes, before 
its bed has quite reached the level of the lower end of the stream. What I 
have called the baselevel would, in fact, be an imaginary surface, inclining 
slightly (1875, 204). 
In a later paper he said again : 
It will be understood that the land plain which is brought down to 
the level of the sea has its margin on the seashore, and that it extends 
back from the shore a distance which may be miles or hundreds of miles. 
As it stretches back, its surface rises slightly. The whole plain is not 
