-75- 
curve representing a line of invasion on the talus. Since 
the width of the talus depends on the height of the escarp¬ 
ment, the line of invasion extends high at low points in 
the range. 
Suocessional continuity on the talus is more 
or less broken, at least in the earlier stages. Lichens 
and certain moss species are undoubtedly important, but 
Betula alba var. papyrifera is one of the noteworthy pioneers 
adapting itself to unuaually severe conditions. This is 
followed sooner or later by aspens, after which there is a 
gradual transition toward the mesophytic climax. 
As the cliff wears down the summit of the range 
will eventually be claimed by the mesophytic forest. At 
present the xerarch series forms a connecting link between 
the maple climax in the valley and on the north side of the 
summit. 
The lower edge~ of the mesophytic forest below 
the talus forms an abrupt border to the flood plain of 
Carp River. This is due to periodical flooding, which 
produces irregularities and telescoping throughout the 
hydrarch series on the comparatively flat floor of the 
valley. Any marked building up of the mesophytic climax 
from this source must therefore await a change in physio¬ 
graphic conditions along the river valley. This will 
