1?6 
and silica. They likewise contain much oxide of 
iron and gypsum, both of which may be derived 
from the decomposition of the pyrites, so abundant 
in chalk. 
Different specimens of peat that I have burnt, 
from the granitice and schistose, soils of different 
parts of these islands, have always given ashes 
principally siliceous and aluminous ; and a specimen 
of peat from the county of Antrim gave ashes 
which afforded very nearly the same constituents 
as the great basaltic stratum of the county. 
Poor and hungry soils, such as are produced 
from the decomposition of granitic and sandstone 
rocks, remain very often for ages with only a thin 
covering of vegetation. Soils from the decompo- 
sition of limestone, chalks, and basalts, are often 
clothed by nature with the perennial grasses ; and 
afford, when ploughed up, a rich bed of vegetation 
for every species of cultivated plant. 
Rocks and strata from which soils have been de- 
rived, and those which compose the more interior 
solid parts of the globe, are arranged in a certain 
order ; and as it often happens that strata very dif- 
ferent in their nature are associated together, and 
that the strata immediately beneath the soil contain 
materials which may be of use for improving it, a 
general view of the nature and position of rocks 
and strata in nature, will not, I trust, be unaccept- 
able to the scientific farmer. 
Rocks are generally divided by geologists into 
two grand divisions, distinguished by the names of 
/ primary and secondary . 
The primary rocks are composed of pure crys- 
