Re-elevation of the Cordil-
leran region to a level probably
as high as or somewhat higher
than the present. Maximum of
second period of glaciation.
REGION OF THE GREAT PLAINS.
Correlative subsidence and
submergence of the great plains,
with possible contemporaneous
increased elevation of the Lau-
rentian axis and maximum de-
velopment of ice upon it. De-
position of the lower boulder-
clay of the plains.
Correlative elevation of the
western part, at least, of the great
plains, which was probably more
or less irregular and led to the
production of extensive lakes in
which interglacial deposits, in-
cluding peat, were formed.
Correlative subsidence of the
plains, which (at least in the
western part of the region) ex-
ceeded the first subsidence and
extended submergence to the base
of the Rocky Mountains near the
forty-ninth parallel. Formation
of second boulder-clay, and (at a
later stage) dispersion of large
erratics.
126



MAN AND THE GLACIAL PERIOD.
Partial subsidence of the Cor-
dilleran region, to a level about
3,500 feet lower than the present.
Long stage of stability. Glaciers
of the second period considerably
reduced. Upper boulder-clay of
the coast probably formed at this
time, though perhaps in part dur-
ing the second maximum of gla-
ciation.
Renewed elevation of the Cor-
dilleran region, with one well-
marked pause, during which the
littoral stood about 200 feet lower
than at present. Glaciers much
reduced, and diminishing in con-
sequence of general amelioration
of climate towards the close of
the Glacial period.
Correlative elevation of the
plains, or at least of their west-
ern portion, resulting in a condi-
tion of equilibrium as between
the plains and the Cordillera,
their relative levels becoming
nearly as at present. Probable
formation of the Missouri co-
teau along a shore-line during
this period of rest.
