CHAPTER V 



ASSOCIATIONS OF ROCKS AND SCREES 



The limestone cliflfs : limestone screes. Sandstone rocks and screes. 

 Are the plants of cliflfs 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 



