2 TRAP-FLORA OF RENFREWSHIRE. 
At any rate, the lines of cliffs or escarpments follow pretty 
closely the arrows on the geological map, which show the direction 
of the glaciation. There is one series showing that part of the 
ice travelled in the direction from Kilmacolm to Lochwinnoch, 
and another approximately from east to west, which corresponds 
with the escarpments of Braes and of the cliffs on the south of the 
Gryffe valley above Carruth. 
The rivers and streams have acted on this roughly outlined and 
rocky country, producing an extraordinary surface of rough, rocky 
bosses, outliers or islands of rock, with sloping, grass-grown 
surfaces above and below; sometimes they look like waves of 
ground breaking in steep, rocky faces. Except in a few valleys 
there is no flat ground whatever. 
Botanically, the country is very rich. Members of the Society 
would find many exquisite places for excursions which do not 
seem to be generally known. The Maisch, Garnock, Calder, 
Millburn, Bridesburn, Blacketty, Green-water, and Gryffe are good 
botanical ground, but it is especially in those problems that arise 
from the presence together of rock, marsh, and natural woodland 
that it is interesting ; and it is with one of these problems that 
this paper is concerned. 
One sees these escarpments or cliffs of rock in every stage of 
development. Sometimes they are bare and scarcely touched by 
vegetation. Others are broken into small projecting boulders. 
Others, again, are covered by rough vegetation. Sometimes, 
though rarely, they have the same piants as the fields around 
them, and then they are only recognised by their slope which is 
steeper than that of the rest of the field. 
By studying the various exposures in different localities, it is 
comparatively easy to see what has happened. ‘The rock faces 
become gradually covered over by vegetation until, eventually, 
they are mere slopes barely distinguishable in a field by a 
steepness and shape which show their origin. The stages of 
covering may be roughly classified as follows :— 
1. The lichen crust.—Bare rocks covered by a nearly 
continuous film of crustaceous lichens with flowering 
plants only in the cracks or crannies of the rocks. 
2. The moss-moor and rangiferina moors.—More or less 
combined with cranny plants. 
