580 FRANK CARNEY 
another invasion of ice, except in the case where ice-erosion had fallen 
short of the unweathered zone. The part of this earlier sheet remain- 
ing should have its original color, or at least the color which it had 
just previous to being overridden. Its present color need not neces- 
sarily be fresh or untarnished, but there is strong presumptive 
evidence that no color alteration has occurred since the retreat of 
the Wisconsin ice which furnished the débris for a protective burial 
of this older drift. 
TOPOGRAPHY OF THE FINGER LAKE REGION 
General statement.—The wide, prevailingly mature, lake-bearing 
valleys of central New York have received critical attention from 
workers in many lines of geology. Less attention, however, has been 
given to the more mature defunct valleys generally transverse to these. 
It is the unusual parallelism of the former, and their marked scenic 
beauty resulting from the variously interrupted drainage history, that 
impel the comment of even the untrained observer. These long 
valleys opening to the north were occupied during the waning stage 
of the ice-sheet by valley glacierst or by valley lobes which were rela- 
tively broad—a condition due to the iceward slope of the valleys. 
Topography favors both ice-erosion and ice-stream aggradation.— 
These conspicuous valleys, digital-like in arrangement, because of 
their general north-south trend, molded the basal ice of the deploying 
sheet into forms that expedited erosion. Furthermore, the fact that 
these valleys sloped toward the overriding wedges of ice facilitated 
the acquiring of a load which in turn augmented the erosive power of 
the ice up to the time when the amount of this load became so great 
that the basal ice lost in velocity; it then did little degradational 
work. In consequence of this differential erosion we find that approxi- 
mately the southern thirds of these valleys are zones of ice-aggrada- 
tion. Therefore Professor Tarr’s goo-foot-contour upper limit of 
most active erosion? defines a plain which dips into the Allegheny 
Plateau. The present attitude of this plain of erosion embodies some 
post-glacial deformation due to warping; but, neglecting the effects of 
tH. L. Fairchild, American Journal of Science, Vol. VII (1899), pp- 252, 253- 
2 Popular. Science Monthly, Vol. LXVIII (1906), p. 389. 
