THE LICHENS OF SOUTH LANCASHIRE. 99 
the stone was turned over or buried by slipping of the ground. No doubt, 
whenever a fresh surface is exposed it is quickly occupied by these small 
Lecideæ and Verrucarie, which seem rapidly to develop. 
LITTORAL Districr.—On the coast, and in the low-lying country adjacent 
thereto, with the exception, of course, of those parts close to the large towns, 
lichens are more frequent and flourish better than in the smokier districts 
inland in Hast Lancashire. This is doubtless due to the fact that westerly 
winds are more prevalent than easterly winds, westward being the direction 
in which the air is purer than in any other, and the direction from which the 
strong winds blow. Nevertheless, the smoke from the large towns of Liver- 
pool, Southport, Warrington, Wigan, Widnes, and St. Helens is sufficient to 
impair the atmospheric purity over the whole district to a very considerable 
extent, gauged by its influence on certain classes of lichens. 
On an analysis of our list we find that 22 per cent. of the species occur 
within two miles of the sea, but they are mostly either terricole species or 
occur on mortared walls.  Rupestral species are relatively few in number, 
and corticole lichens mainly occur only under special conditions. 
The coast-line of South Lancashire is about 48 miles long. Only about 
19 miles of the coast are, however, really maritime ; the remainder, situated 
in the estuaries of the Mersey and Ribble, is purely estuarine in character. 
The low flat coast, with its limited amount of rock, is not favourable for 
lichens. In the estuarine portions it consists mainly either of salt-marsh and 
mud-flats, which are naturally destitute of lichens, or of steep banks of glacial 
clay, which weather too rapidly to permit much in the way of lichen-growth. 
The maritime portion of the coast consists of a sandy shore backed by an 
extensive tract of sand-dunes, the lichen-flora of which is of particular 
interest and will be described presently. 
Coastal Rocks.—The only rocks on the coast are two outcrops of Bunter 
Sandstone, namely, at Dingle Point and Hale Point, both in the Mersey 
estuary. ‘These rocks have a very poor lichen florula, for the polluted air, the 
muddy water which washes them, and the friable nature of the rock itself, are 
all inimical to lichen-growth. On the rocks at Dingle Point, which is situated 
at the south end of Liverpool, close to the docks, the only lichens we have 
seen are a little Lecanora campestris, Nyl., on hard “ fault rock," and Cladonia 
Jimbriata on mossy rocks. All the bare rock below high-water mark is mud- 
coated, whilst the rocks above tide-level, apart from any question of smoke 
influence, are too friable for lichens. An adjacent sea-wall, built of harder 
sandstone, yields a few lichens on the sandstone blocks and on the cement, 
namely, Lecanora campestris, Nyl., L. atrynea, Nyl., L. umbrina, Nyl., 
L. atra, Ach., апа Callopisma vitellinum, Sydow. On the low rock outcrop 
known as Hale Point, a few lichens still linger, although the place is only 
turee miles from the great chemical manufacturing town of Widnes. These 
