Chap. IV.] 
MISCELLANEOUS. 
141 
generality of cases, that, owing to the resistance 
of the subsoil, the progress of the root upward 
is equal to nearly the whole of the growth in 
diameter; and that, in proportion as the deposit 
of new growth below the root decreases from 
mechanical pressure, the new deposit above the 
root increases. I have seen ash-trees growing 
on gravel with the roots all round them above 
the ground to an extent of double the length of 
the boughs. 
Where cattle do not come, and where the 
surface is not liable to denudation, as turf or 
pavement, the ground may be observed to be 
raised about the roots of trees by this lateral 
upward growth of the roots. Where cattle do 
come the case may be altered. Cattle use trees 
as rubbing-posts, and as refuges from flies, the 
sun, wind, or rain. Under such circumstances, 
the ground, instead of being raised, is often worn 
into hollows around trees: for, the herbage 
being worn away, in drought the earth is blown 
away as dust, and cattle paw and cast it up 
with their feet to drive the flies from them; in 
wet weather, the earth is carried away on the 
feet of the cattle. This, and the eternal disposi¬ 
tion of roots to rise by lateral growth in girthing, 
bring them in contact with the feet of cattle, 
