To6 STUDIES FOR STUDENTS. 
taken to mean a sloping surface. It may be more appropriately 
called a graded valley plain, or a graded valley floor, for these 
terms do not contain any implication that the surface is either 
low or level. 
Another objection to the above use of ‘‘ baseleveled surface”’ 
is that it arbitrarily separates graded valley floors and graded 
hill sides, whose analogies with respect to the processes of 
gradation ought to be exhibited rather than concealed in a sys- 
tematic terminology. It can hardly be supposed that anyone 
would today call a waste-covered hillside a ‘baseleveled sur- - 
face,’ although it has every characteristic with respect to the 
processes of gradation that is possessed by a graded valley 
floor. A third objection to this use of ‘‘baseleveled surface”’ 
would be found when applying it to the High plains of eastern 
Colorado and western Kansas, which, according to the explana- 
tion offered by Johnson and cited above, were produced by 
aggradation during a time of less rainfall than at present. Here 
an extended surface was, as Hayes might phrase it, ‘‘ brought 
approximately to a baselevel, either general or local, by the pro- 
cesses of gradation,’ and yet it was actually built up hundreds 
of feet above the pre-existent and the present valleys, and thou- 
sands of feet above the general baselevel, although there is no 
indication of any discontinuity in the graded surface between 
the High plains and the mouths of their aggrading rivers. The 
High plains are better called aggraded river-made plains, or 
fluviatile plains; and in this respect they resembled the great 
plains of northern India. 
The geographical cycle—The period of time during which an 
uplifted land mass undergoes its transformations by the pro- 
cesses of land sculpture, ending in a low featureless plain, has 
been called a geographical cycle, or, as Lawson phrases it, a 
‘geomorphic cycle” (253). Hayes writes: ‘The term grada- 
tion period is employed for the entire time during which the base- 
level remains in one position ; that is, the interval between two 
elevations of the earth’s surface of sufficient magnitude to pro- 
duce a marked change in the position of sea level”’ (22), 
