[034]

THE history of the earth forms a large and complex subject of enquiry, divisible at its outset, into two distinct branches; the first, comprehending the history of unorganized mineral

Higgins on the Mosaical and Minem'al Geologies, 1832;and more especially to Professor Sedgwick's eloquent and admirable discourse on the Studies of the University of Cambridge, 1833, in which he has most ably pointed out the relations which Geology bears to natural religion, and thus sums up his valuable opinion as to the kind of information we ought to look for in the Bible:

" The Bible instructs us that man, and other living things, have been placed but a few years upon the earth; and the physical monuments of the world bear witness to the same truth: if the astronomer tells us of myriads of worlds not spoken of in the sacred records; the geologist, in like manner, proves (not by arguments from analogy, but by the incontrovertible evidence of physical phenomena) that there were former conditions of our planet, separated from each other by vast intervals of time, during which man, and the other creatures of his own date, had not been called into being. Periods such as these belong not, therefore, to the moral history of our race, and come neither within the letter nor the spirit of revelation. Between the first creation of the earth and that day in which it pleased God to place man upon it, who shall dare to define the interval? On this question scripture is silent, but that silence destroys not the meaning of those physical monuments of his power that God has put before our eyes, giving us at the same time faculties whereby we may interpret them and comprehend their meaning."

[035] 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,

[036 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 con tinued 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 deposits has resuIted chiefly from the mechanical action of moving water, and has occasionally been modified

[037 GEOLOGICAL ENQUIRY.] 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, 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.

[038] 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.