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TRAP-FLORA OF RENFREWSHIRE. 9 
Young plants of both show the trefoil leaves, and compete with 
grasses and ordinary flowering shrubs. Later on they are above 
the grasses and lose these trefoil leaves, becoming either (broom) 
leafless or (whin) spiny leaved. Both are xerophytic finally, but 
at first mesophytic. 
What I think both Warming and Schimper scarcely appreciate 
is the change that is always at work in all vegetation. They look 
simply to the present plant covering, and so classify the world’s 
vegetation by its present condition, just as, in a geological map, 
one simply takes the surface rock. 
It would be, I think, more scientific and more easy to carry out 
the geological comparison a step further. We have, in these 
rock faces, outliers of the previous vegetation of the country. 
In the rings of different plants round an exposed boulder we 
have an exposure of the successive vegetations. We can see 
before our eyes not merely what is going on now, but what has 
possibly happened all over Britain since the Ice Age. 
Then, no doubt, the lichen-moors and moss-moors covered 
Square miles of country, as they do in the far north to-day. 
There was probably a Vaccinium or moor state, and after this 
came broom and whin, followed by roses, which again was 
followed by woods. 
It is quite unnecessary to suppose great changes of climate. A 
dry, warm, steppe-like climate is assumed by Magnin to have 
marked the close of the Ice Age. This is quite unnecessary. 
The conditions would only permit dry plants like whin and 
broom to grow. 
At any rate, that is my present opinion ; and this conception of 
the rock faces as showing the stages by which bare, bald and 
rugged rocks are changed into peaceful, grassy lowlands or fine 
beech and oak wood, seems to me well worth close investigation. 
