J$(j PROPER SUBJECTS OF
and to have undergone no alteration in their
nature and qualities; but to have been submitted
at their creation to the self same laws that
regulate their actual condition, and to have continued
subject to these laws during every succeeding
period of geological change. The same
elements also which enter the composition ol
existing animals and plants, appear to have
performed similar functions in the economy ol
many successive animal and vegetable creations.
,
In tracing the history of these natural phenomena
we enter at once into the consideration
of Geological Dynamics, including the nature
and mode of operation of all kinds of physical
agents, that have at any time, and in any
manner, affected the surface and interior of the
earth. In the foremost rank of these agents, we
find Fire and Water,—those two universal and
mighty antagonizing forces, which have most
materially influenced the condition of the globe;
and which man also has converted into the most
efficient instruments of his power, and obedient
auxiliaries of his mechanical and chemical and
culinary operations.
The state of the ingredients of crystalline
rocks has, in a great degree, been influenced
by chemical and electro-magnetic forces; whilst
that of stratified sedimentary deposits has resulted
chiefly from the mechanical action of
moving water, and has occasionally been moditied
by large admixtures of animal and vegetable
remains.
As the action of all these forces will be rendered
most intelligible by examples of their
effects, I at once refer my readers for a synoptic
view of them, to the section which forms the first
of my series of plates.* The object of this section
is, first, to represent the order in which
the successive series of stratified formations are
piled on one another, almost like courses of
masonry ; secondly, to mark the changes that
occur in their mineral and mechanical condition
; thirdly, to show the manner in which all
stratified rocks have at various periods been
disturbed, by the intrusion of unstratified crystalline
rocks ; and variously affected by elevations,
depressions, fractures, and dislocations ;
fourthly, to give examples of the alterations in
the forms of animal and vegetable life, that have
accompanied these changes of the mineral conditions
of the earth.
From the above section it appears that there
are eight distinct varieties of the crystalline unstratified
rocks, and twenty-eight well defined
divisions of the stratified formations. Taking
the average maximum thickness of each of these
divisions, at one thousand feet,f we should have
* The detailed explanation of this section is given in the description
of the plates in vol. ii.
+ Many formations greatly exceed, whilst others fall short, of
the average here taken.