22 
MUSEUM BULLETIN NO. 23. 
that of differential warping. The rate of warping increases 
towards the north but is interrupted by local irregularities. 
The marked change in the direction and rate of uplift in the 
northern part of the district seems to show that there is a sort 
of “hinge line” or zone here; the region north of this line or 
zone was affected by epeirogenic movements which did not affect 
or only slightly affected the region south of it. The direction of 
maximum uplift, which was the result of the later set of move- 
ments, was more nearly north than that of the earlier uplift. 
