30 I’UOPER SUBJECTS OF 
and to have undergone no alteration in their 
nature and qualities ; but to have been sub- 
mitted at their creation to the self same laws that 
regulate their actual condition, and to have con- 
tinued subject to these laws during every suc- 
ceeding period of geological change. The same 
elements also which enter the composition of 
existing animals and plants, appear to have 
performed similar functions in the economy of 
many successive animal and vegetable crea- 
tions. 
In tracing the history of these natural phe- 
nomena we enter at once into the consideration 
of Geological Dynamics, including the nature 
and mode of operation of ail 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 
ffnd 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 re- 
sulted chiefly from the mechanical action of 
moving water, and has occasionally been modi- 
