altitude of 
ijooo feet to 
500 feet or 
less. The 
relation of 
this terrace 
to the drain¬ 
age suggests 
that it is a 
remnant of 
a pre -glacial 
valley floor, 
and if so it 
may be a 
grade plain 
contempora¬ 
ry with the 
low pene¬ 
plains, 
These fea¬ 
tures point to 
a long con¬ 
tinuance of 
base-level at 
approxi m- 
ately its pres¬ 
ent height, 
the time be- 
ing subse¬ 
quent to the 
uplift of the 
older pene¬ 
plain. It was 
probably 
during this 
