10 Principles of Geology. 
of wide-spread formations; and finally combining together observa- 
tions made in distant regions, we ascend to a grand principle of uni- 
versal analogy in the construction of our planet. If, then, such anal- 
ogy pervades the structure of different regions, it will be necessary, 
in stating general laws, to call in the aid of extensive research; but 
particular laws for each country can only be derived from local in- 
vestigation. 
Possibly those who are accustomed to trace across our island the 
wonderful regularity of strata, or who know the strong resemblance 
which they exhibit in countries far removed from each other, may 
have expected more sweeping assertions than I have thought it correct 
to maintain. ‘They might, perhaps, have been little surprised at a 
bold declaration, that all our secondary rocks may be discovered 
with their proper characters over all the continent, when the labors 
of foreign geologists have been as successful as our own. But this 
would be an unjust view of the matter; in several instances it is ab- 
solutely disproved. ‘The utmost that can be expected, is to trace a 
general conformity and universal analogy of deposits. To what ex- 
tent this conformity reaches, much as geologists have done, they have 
not yet demonstrated. It is ascertained that there are certain for- 
mations which possess a mineralogical character, and a geological 
position so uniform in all parts of the world, as to allow no doubt of 
their cotemporaneous origin, and even in some of their subordinaje— 
beds an astonishing affinity prevails; but neither these beds, nor the 
formations themselves, are in all places, continuous in extent, nor con- 
stant in thickness, nor identical in chemical composition. Hence 
arise differences in the geological structure of different countries, 
and the more distant from each other the points of comparison, the 
less perfect is the agreement of the rocks. Some writers, overlook- 
ing these differences, have erroneously asserted the universality of 
formations ; others, not understanding the simple and beautiful gra- 
dation of nature, have absurdly denied the regular “construction of 
our planet. 
THE ORGANIC FOSSILS commonly found in the earth are plants, 
corals, crusts of radiaria, shells of mollusca, the hard coverings of 
crustacea, scales and bones of fishes ; reptiles, cetacea, birds, and 
mammiferous quadrupeds. From very early times, the wonder of 
mankind has been excited by those fossil shells which are inclosed 
