-42 
involves an examination of the environmental factors and 
plant successions (1) at the summit (2) along the escarp¬ 
ment (3) on the talus slope (4) below the talus slope* 
(l) Summit of the range. 
fa) Ecological factors. In general, 
the forested area of the north slope may fall short of 
reaching the crest of the ridge, as shown in fig. 26, E, 
or may reach slightly over the summit, as at F. From 
this point to the brink of the precipitous cliff, which 
averages from 20 - 40 m., there is usually a large amount 
of bare rock surface. Where the soil has accumulated, it 
is of very slight depth. There seem to be two principal 
reasons for this condition, both being due to the presence 
of the escarpment; fl) the soil due to rock disintegration 
is washed over the south side of the crest nearly as fast 
as it is formed, (2) the escarpment itself forms an effectual 
barrier to the encroachment of the mesophytic forest below. 
This zone of bare or nearly bare rock surface therefore re¬ 
mains unprotected. Its exposed situation makes it especially 
susceptible to the dynamics of weathering, including the 
frost of winter, the heat of summer, full exposure to rain 
and to all winds from the south. A portion of the soil 
wafefced over the crest accumulates in a narrow strip along 
the top of the talus slope. The rest is gradually washed 
