SOIL OF THE GRAUWACKE ROCK. 47 
The soil of the greywacke rock, is highly fertile, 
perhaps as much so as slate and sandstone, for the 
productiveness of which, there would seemingly be 
so good a reason, im their far looser texture, and 
fissility, giving transit. to evaporations during the 
droughts of the summer months. The depth ofa 
superstratum ought never to be lost sight of how- 
ever, in searching for the causes of the fertility of a 
given rock. Many farmers complain that slate lands 
scorch sooner than limestone tracts, a complaint 
contrary to all rule, as well as to reason, and will be 
found dependent on, the soil of thezr estates being 
shallower even than that, usually known to cover 
lime-rock. It is perfectly astonishing to observe, 
that. though soil gives a manifest advantage to 
the growth of all timber by its accumulation of 
carbon, water, &c. for their support, yet, that the 
nature of the rock below, interferes but in a trifling 
way with their development, so far as respects their 
taking root and fixation. Most wonderfully do trees 
contrive to bore and insinuate their roots into even 
such strata as the grauwacké and greenstone; on 
examining attentively where their roots happen to 
be exposed in such rocks, a sort of mouldering and 
decay of the stone appears, and the conclusion thence 
drawn, is that though by their contortions, these 
members. were probably long resisted in their efforts 
to descend, a slow, but continued erosion and dis- 
solution of the components of the dense material 
was effected, and thus, greater and greater scope 
given by this extraordinary operation of vitality, 
for the enlargement of these portions of the tree, 
and the introduction of soil and other supplies 
from above. 
LIMESTONE. 
Guided by prevalence in quantity, limestone 
comes next under consideration after slate and 
