122. Hayes and Campbell—Appalachian Geomorphology. 
point on the surface be taken its relations to sealevel may be 
so represented. A point on the present site of Chattanooga has 
been selected as fairly representative and where the various alti- 
tudes can be well determined. These relations are represented in 
the diagram, figure 1, page 99. The vertical lines divide the space 
into five time divisions. These divisions are only approximately 
proportional to the time, the late divisions being much too large 
and the earlier divisions too small. Taking the horizontal line 
at the base of the diagram as sealevel, the full line represents 
the altitude of the main stream channels and the dotted lines 
their altitudes at former periods marked by the remnants of 
baselevel peneplains still existing. The upper dotted line L in 
the diagram indicates the position of the original land surface 
with reference to sealevel. Its distance above the present land 
surface at the right of the diagram corresponds with the thick- 
ness of strata removed by erosion from the point taken, which 
is on an anticlinal fold and hence upon rocks low in the series. 
The thickness of the rocks eroded is only represented approxi- 
mately, since the original thickness of the Carboniferous is not 
known. The line K represents the altitude of the land surface 
slowly approaching sealevel by degradation during the long 
cycle of Cretaceous baseleveling. It is scarcely probable that 
the land remained stationary during this long period. There 
were doubtless minor oscillations, but these have left no record 
upon the surface and hence cannot be represented. Atthe close 
of the Cretaceous cycle came the elevation of the surface shown 
by the rise in the line K at the beginning of the second time 
division. With the elevation, the line K ceases to represent the 
stream level which is indicated by the heavy line 7, diverging 
from K at first rapidly and then slowly, the peneplain being 
developed during the Tertiary cycle. Since this cycle was not 
so long as the preceding and the baseleveling not so complete, 
the line T does not approach so near sealevel as the line K. 
During the third period, which was one of depression, the lines 
K and 7 remain parallel, since little, if any, erosion was taking 
place at Chattanooga at that time. With the elevation at the 
end of the Lafayette depression the line 7'in turn ceases to rep- 
resent the stream level which is indicated by the line P, and this 
diverges continually to the present except during the Columbia 
depression. Thus the various lines at the right of the diagram 
indicate the position of various plains of erosion with reference 
