THE LICHENS OF SOUTH LANCASHIRE. 95 
deposits than it would be if situated in a smokier district. Nevertheless, it 
is certain that the lichen-flora of the limestone more closely approaches the 
normal than does that of the siliceous rocks in the same district. The lichens 
of the Carboniferous Limestone will be dealt with more fully in the next 
part of our paper. It may be added that 32 per cent. of our total species 
are restricted to caleareous substrata. 
B. Condition of the Lichen- Flora in the various Districts. 
Whilst there is no part of South Lancashire in which the effects of atmo- 
spheric pollution are not felt, yet some of our districts are much less affected 
than the others ; and corresponding differences can be readily detected in 
the condition of the lichens. 
* Hast LANCASHIRE.’—Our smokiest district is that situated in the south- 
eastern part of the vice-county, with Manchester at its centre, and comprising 
Oldham, Ashton-under-Lyne, Stockport, Stalybridge, Rochdale, Bury, and 
other smaller towns. A considerable portion of this area is purely urban in 
character, and is now destitute of lichens, whilst much of the remainder, 
owing to the close proximity of the towns to each other, may be called inter- 
urban. As a matter of fact, the whole district lying between Blackburn, 
Accrington, and Burnley on the north, and Wigan, Bolton, and Manchester 
on the south, is far too much affected by smoke to permit of anything 
approaching normal lichen-growth. The distribution of towns in “ East 
Lancashire " is such that no part of the area is more than five miles from a 
large town. Furthermore, from whichever direction the wind blows, it 
brings smoke ; during westerly winds the area receives smoke from all that 
part of South Lancashire lying to the west, whilst, with easterly winds, 
smoke is brought from the large manufacturing towns of the West Riding 
of Yorkshire. As a consequence, in this district the lichen-flora is practically 
in eatremis ; corticole species are absent, and, as will be gathered from our 
remarks under Section A, rupestral, and even terricole, species are very 
badly affected. 
On the western side of this smoky area, in the hills about Chorley, 
Rivington, Parbold, and Billinge, a slight improvement in the condition of 
the lichens is manifest, but a more marked improvement will be found when 
we travel northwards, and reach the Forest of Pendle and the Ribble Valley. 
“RIBBLE VarrLEY."—Our best district for lichens is a narrow strip of 
country in that part of the Ribble Valley lying along the northern part of 
Pendle Hill, for there the influence of smoke is least felt, and calcareous 
rocks occur. It is owing, in a large measure, to the numerous species found 
exclusively in this small tract that the lichen-flora of South Lancashire is 
redeemed from utter poverty. 
