LATE PLEISTOCENE OSCILLATIONS, 
9 
In the southern part of the basin altitudes of the shore-line are 
not definitely determinable because, apparently differential 
uplift caused a transgression of and a cutting away of the original 
shore-line in this part of the basin. The altitudes of this beach 
are not sufficiently numerous to accurately determine the direc- 
tion of maximum uplift and rate of tilt, but they show, ap- 
proximately, that the differential uplift which affected this area 
during the life of and after the disappearance of the lake was 
greatest in a nearly due north direction and that the rate of tilt 
is about 3 feet per mile over part of the basin. The high rate 
of tilt as shown by the deformation of this beach is remarkable 
when it is considered that the present altitudes of the beach 
record only the differential uplift which took place during the 
latest stages of the marine submergence. It also shows that the 
region north of the Ottawa river was probably affected by a 
greater amount of uplift than has affected the Ottawa region. 
It is known that the direction of maximum uplift over a 
great part of the Great Lakes region is in a direction about north 
20 degrees east. The change of direction to nearly north in the 
Ottawa valley nearly coincides with the direction of general 
glaciation. This supports the view that the uplift of the land 
was due to isostatic readjustment following the removal of the 
burden of the ice-sheets, which theory has at least a high degree 
of probability to support it. 
Character of the Champlain Clays. 
The Champlain or Leda clays, as they were named by J. W. 
Dawson, have long been known to be widespread in the Ottawa 
valley and to have a maximum thickness, in places, of nearly 
200 feet. They are exposed in numerous sections in the vicinity 
of Ottawa, at various altitudes from 130 feet, in the lowest part 
of the Ottawa valley, up to 600 feet above sea-level, the highest 
locality at which they are known to occur being in the stream 
valley leading up to Kingsmere from the east. 
In physical character the clays are markedly different in 
their upper and lower portions. The lower portion is a sandy 
and silty clay often well laminated, especially towards the base. 
