CHAPTER V 
ASSOCIATIONS OF ROCKS AND SCREES 
The limestone cliffs: limestone screes. Sandstone rocks and screes. 
Are the plants of cliffs and screes lithophytes ? 
THE LIMESTONE CLIFFS 
LIMESTONE cliffs are very numerous in the district, and 
some of the gorges, as the one known as the Winnats, near 
Castleton, are two hundred feet (61 m.) deep. It appears to 
be generally accepted among geologists that such limestone 
gorges represent ancient underground water-ways whose roofs 
have collapsed. 
On the damper and more sheltered cliffs, ferns and flowering 
plants occur in the crevices and on the ledges. Most of these 
plants are members of the neighbouring plant associations, such 
as ash woods, scrub, and calcareous pastures. Near villages, as 
on the cliffs near Middleton at the foot of Middleton Dale, 
several alien plants have established themselves. The richness 
of the vegetation of the limestone cliffs varies with their 
dampness, the damper cliffs being rich in species, the driest 
ones extremely poor. The dampness or dryness of the cliffs 
is largely determined by the dip of the strata; and hence, in 
any gorge, the rocks on one side are usually richer in plants 
than the rocks on the opposite side. For the same reason, the 
vegetation of the opposite sides of a valley may vary some- 
what in character. Aspect alone does not usually appear to 
be a fundamental differentiating factor, except in the case of 
species at or near their limit of distribution. 
In the following list of the more characteristic plants 
