THE LICHENS OF PERTHSHIRE 3 
pee? of their ose by the mountains — become, by com- 
pies on and co ae. liberation of heat, drier and drier as 
Shey. dpotoush Strathm The annual rainfall about Perth and 
Coupar Angus only Secale about 30 in., whilst at Loch Katrine 
M 
it is 78 in., and in some of the mountain glens round Ben More 
and Ben Laoigh it equals = exceeds 100 in. With easterly winds, 
on the contrary, the west of Perthshire is relatively dry, the 
heaviest rainfall then being found in the eastern upland region 
about cei Shee and Strath Ardle. 
mount of snowfall on the mountains is often very great, 
f 
the oneal would appear to have a marked effect on his distribu- 
tion of certain sa The relative rareness in the west, for 
instance, of most species of Alectoria, . ae ep with the east, 
is a noticeable feature ; aed Ist, on the other hand, members of the 
Sticta group attain a great adc in ee wooded glens of the 
west, and are either absent from or very poorly developed in 
similar ares in the east. 
A word may here be said with regard to the mary effect 
of atmospheric pollution on Perthshire lichens. No part of the 
county comes within the manufacturing district of the Scottish 
la of which great smoke-producing area the towns of 
Motherwell and Coatbridge are familiar examples; but when 
erly winds are blowing, the smoke from this district forms a 
au iL leaden haze over all South Perthshire. Even in the extreme 
north of the county it renders the distant landscape ae a 
when otherwise it would be clear. The effect of the smoke on 
bark- loving lichens is, unfortunately, quite iicetatts about 
Rumbling Bridge and Dunblane, and in a less degree further 
such common species as Hvernia prunastri and Parmelia physodes 
being small and phous develope ed. “yma Siig grow on rocks 
and walls also show diminution of s u a less extent. 
Happily we have ice no signs of pofiane in ne central and 
northern parts of the county. 
GEOLOGY. 
In the Sette short sketch .. the geology, we do not pro- 
pose to do more than simply indicate in a general w 
osi- 
tion and outcrop of the various rea a detailed vie oo 2 
the geological structure being out of place here, 99 quite un 
can orl from the point of view of the oe 
As before stated, Perthshire is divided n sao ag wo 
portions the Highlands and the iawlndsoaie anldon, ‘bing 
marked by a great geological fault which traverses the county 
from es to south-west. Along this line the ancient crys- 
talline schists, of which the Highlands are largely composed, 
