Geology and Mineralogy considered with reference to Natural Theology/Chapter 3
Proper Subjects of Geological Inquiry.
The history of the earth forms a large and complex subject of inquiry, divisible at its outset, into two distinct branches; the first, comprehending the history of unorganized mineral matter, and of the various changes through which it has advanced, from the creation of its component elements to its actual condition; the second, embracing the past history of the animal and vegetable kingdoms, and the successive modifications which these two great departments of nature have undergone, during the chemical and mechanical operations that have affected the surface of our planet. As the study of both these branches forms the subject of the science of Geology, it is no less important to examine the nature and action of the physical forces, that have affected unorganized mineral bodies, than to investigate the laws of life, and varied conditions of organization, that prevailed while the crust of our globe, was in process of formation.
Before we enter on the history of fossil animals and vegetables, We must therefore first briefly review the progressive stages of mineral formations; and see how far we can discover in the chemical constitution, and mechanical arrangement of the materials of the earth, proofs of general prospective adaptation to the economy of animal and vegetable life.
As far as our planet is concerned, the first act of creation seems to have consisted in giving origin to the elements of the material world. These inorganic elements appear to have received no subsequent addition to their number, 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 of existing animals and plants, appear to have performed similar functions in the economy of 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 deposites has resulted chiefly from the mechanical action of moving water, and has occasionally been modified 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 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, we should have a total amount of more than five miles; but as the transition and primary strata very much exceed this average, the aggregate of all the. European stratified series may be considered to be at least ten miles.
- 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.