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 2? a 
S. Andreaea Rothii S. R. heterostichum 
S. A. crassinerva R. lanuginosum 
S. A. alpina R. canescens 
S. A. petrophylla Phytomitrium polyphyllum 
S. Tetraphis Browniana S. Campylosteleum saxicola 
S. Swartzia montana S. Hedwigia ciliata 
S. Dicranum fuscescens Tortula muralis 
Grimmia apocarpa Eurhynchium murale 
G. pulvinata Leconora, ? sp. 
G. trichophylla Lecidea, ? sp. 
G. Doniana S. Parmelia saxatilis 
S. Rhacomitrium fasciculare S. Pertusaria dealbata 
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 + :-— 
Sphagnum spp. Hypnum Schreberi 
Rhacomitrium lanuginosum tSilene amoena 
Hylocomium spp. tAlchemilla alpina 
