GLACIAL EROSION IN LONGITUDINAL VALLEYS 729 
this relation of valleys here has tended to mollify the general effective- 
ness of ice-corrasion. 
On the uplands striated surfaces again appear. ‘These surfaces 
range from 1,200 to 1,400 feet in altitude, and even above this they 
are to be found on the salients opposed to the direction of ice-motion. 
Averages of several scores of readings made in different localities 
ranging between the 1,200- and 1,400-foot contours give S. 46°- 
48° E. The averages of striae on surfaces still higher give S. 53°- 
61° E. These areas fall within a reach of three miles of the major 
Lref ficient 
Vigorous 
; : 
Cross-section of longitudinal valley showing 
vertical FANGCS 117 1CC-CrOS/O/. 
FViGS Si: 
Fic. 5.—Cross-section of longitudinal valley showing vertical ranges in ice-erosion. 
valley; in the main they are found in the general flat country consti- 
tuting plateau divides. 
Between the two zones of ice-erosion already mentioned, that is 
the areas near the bottom of the major valley and the areas on the 
uplands, lies another zone of least effective ice-work. This is the 
horizon of the folded subjacent strata; in the Owasco valley area it 
is approximately between the rooo- and 1200-foot contours. 
Fig. 5 summarizes these observations. ‘The cross-section is nor- 
mal to the axis of the longitudinal valley, not taking note of the 
deflections of this axis. The matter of altitude in relation to sea- 
level is likewise neglected, as great discordance may exist between 
present-day and Wisconsin“ice-epoch altitudes. So little is known 
definitely about the relation that existed, during Pleistocene time, 
between the land mass of northeastern North America and sea-level, 
and furthermore, the connection between ice-erosion and a base level 
from which altitude is measured, may probably be so slight, that this 
relation, as a factor, may safely be neglected. The topographic 
