V] 



ASSOCIATIONS OF ROCKS AND SCREES 



141 



shelter from the cliffs above them, they have a rather richer 

 flora (see Chapter VII). 



Although a fairly long list of cellular flowerless plants, 

 which occur on the faces of the sandstone rocks, is given below, 

 most of the species are very rare and local ; and it is scarcely 

 possible to single out any vascular plants which, in this district, 

 exhibit any pronounced partiality for living on the sandstone 

 rocks. Many of the cellular cryptogams are very susceptible 

 to the action of smoke (Wilson, 1900); and, as the southern 

 Pennines are situated between two great manufacturing districts, 

 it is highly probable that many of the mosses and lichens char- 

 acteristic of bare rocks are even rarer now than they were a 

 century ago. The following silicolous and saxicolous cellular 

 plants have been recorded (Linton, 1903; Crossland, 1904; etc.) 

 for the sandstone rocks of the southern Pennines : the species 

 which are confined to such rocks are preceded by the letter 

 " S " :— 



Crampton has recently described the vegetation of the 

 screes of Caithness. The plants of these screes are chiefly 

 humus-loving species, such as frequently occur on the sandstone 

 screes of the Pennines ; and there would appear to be little 

 justification for giving the vegetation in question the rank 

 either of " formation " or even " subformation " (Crampton, 

 1911 : 26 and 43). This will perhaps best be seen by quoting 

 all the species mentioned by Crampton. Those which do not 

 occur on the Pennines are indicated by a f : — 



Sphagnum spp. 

 Rhacomitrium lanuginosum 

 Hylocomium spp. 



Hypnum Schreberi 

 tSilene amoena 

 tAlchemilla alpina 



