The original fluidity of the globe appears to be indicated by its present spheroidal form; and in the large planets that compose part of our system, the spheroidal form is more fully displayed, particularly in the planet Jupiter. Now it well deserves attention, that the conditions under which this form was impressed on the earth and planets, cannot recur again by any known causes now in operation, or by any other conceivable cause, except the fiat of the Creator. Thus we are brought, at once, to a commencement of the series of geological changes, which could not have been the result of any secondary causes, that come within the limit of our present experience. About a century ago, it was the fashion among philosophers to explain all the phenomena of nature, even thunder and muscular action, by the operation of known causes; that is, by the established laws of mechanics, and by chemical fermentation. The discoveries of Franklin and others subsequently proved, that there were more things in heaven and earth than had been dreamed of in past philosophy. It would, indeed, be astonishing if, with our limited powers and ephemeral existence, we have now discovered all the causes that have effected changes in the former condition of the globe.

"One part, one little part, we dimly scan

Through the dark medium of life's feverish dream."

The senses given us by the Creator, as the inlets of knowledge, are sufficient for all the useful purposes of life on our planet; but it would be extremely rash to infer, that they are adequate to discover or perceive all the properties of matter, or the changes these properties can effect. Some material powers or agents cannot be made perceptible to any of our senses, except by their effects; such are universal gravitation, magnetism, and crystalline polarity; and ages had elapsed, before the existence or operation of such powers was even suspected. If we extend our views to the planetary system, we may discover a state of things which implies that the elementary matter of which the planets are composed, is essentially different from terrestrial matter; and the difference must be such, that it would require an organization and constitution of the inhabitants (if they be inhabited,) altogether so unlike what we are acquainted with, that we are as incapable of forming any distinct idea respecting them, as a blind man is of forming an idea of colours. This may be clearly inferred from the different density of the planets. The density of Saturn is stated by astronomers to be about one tenth that of the earth, or scarcely half the density of pure water. Most of the Saturnian metals and minerals must be lighter than cork wood; and no fluid like water, can exist any where but in the centre of the planet. But Saturn has an atmosphere and variable clouds or belts; it must therefore have a fluid on its surface, that performs the functions of water; yet this fluid must be chemically and essentially different from water, or from any fluid on our earth. The properties of matter, and the

whatsoever kind, finds its proper resting place, to think that the principles of physical and moral truth can ever be in lasting collision. And as all the branches of physical science are but different modifications of a few simple laws, and are bound together by the intervention of common objects and common principles; so also, there are links, less visible, indeed, but not less real, by which they are also bound to the most elevated moral speculations.

"Geology lends a great and unexpected aid to the doctrine of final causes; for it has not merely added to the cumulative argument, by the supply of new and striking instances of mechanical structure adjusted to a purpose, and that purpose accomplished; but it has also proved, that the same pervading principle, manifesting its powers in our times, has also manifested its power in times long anterior to the records of our existence."

SUPPLEMENT TO CHAPTER VIII.

ON THE GREAT COAL FORMATION.

BESIDE what has been already stated respecting the freshwater origin of the coal strata, I wish the reader to bear in mind, that the marine or freshwater character of formations, must be determined by the general assemblage of the organic remains, and not by a few individuals, or a few species of shells, which differ from the general character of the fossils; particularly as we now know, that several species supposed to be marine, are capable of living in fresh water.

In the great coal formation of England, the upper and middle beds, for many hundred feet or yards in thickness, abound in the remains of terrestrial or of marsh plants with some freshwater shells, but without any admixture of marine species. The whole mass of the coal measures, however, rest on marine limestone; and in some parts of England, the lowest measures alternate with beds of limestone, and also contain some shells supposed to be marine. Though the upper and middle parts of all the English coal fields are freshwater formations, we can have no doubt, that the limestone on which all the coal fields rest was deposited under the ocean; but many circumstances tend to prove, that its elevation was a slow and longcontinued process, and that the lower part of the coal measures was deposited when nearly on a level with the sea, or in situations subject to interruptions of marine water; or else the ground was subject to oscillations, which brought it, at different times, below the level of high tides.

The great valley of the Mississippi contains the largest coal field in the known world; and what is now annually taking place in some parts of that valley, appears to confirm in a remarkable manner, the opinions I have advanced (pages 113 to 118) on the formation of coal and the cause of the frequent recurrence of the same series of strata at different depths, in the same mine; which I attribute to the periodical filling and desiccation of lakes. In the second volume of Mr. Stuart's interesting "Travels in the United States," there is a very instructive account of the Valley of the Mississippi, quoted from an American review. I shall here insert the parts immediately connected with the present subject:

"What is called the Valley of the Mississippi is not in reality a valley, but an extensive elevated plain, without hills or inequalities deserving notice. It extends west from the western slope of the Alleghany Mountains, to the sand plains near the Missouri, a distance of about 1500 miles, and south from the valley of the northern lakes, to the mouth of the Ohio, about 600 miles. No part of the globe possesses such an extent of uniform fertillity. The difference in ele

whatsoever kind, finds its proper resting place, to think that the principles of physical and moral truth can ever be in lasting collision. And as all the branches of physical science are but different modifications of a few simple laws, and are bound together by the intervention of common objects and common principles; so also, there are links, less visible, indeed, but not less real, by which they are also bound to the most elevated moral speculations.

"Geology lends a great and unexpected aid to the doctrine of final causes; for it has not merely added to the cumulative argument, by the supply of new and striking instances of mechanical structure adjusted to a purpose, and that purpose accomplished; but it has also proved, that the same pervading principle, manifesting its powers in our times, has also manifested its power in times long anterior to the records of our existence."

SUPPLEMENT TO CHAPTER VIII.

ON THE GREAT COAL FORMATION.

BESIDE what has been already stated respecting the freshwater origin of the coal strata, I wish the reader to bear in mind, that the marine or freshwater character of formations, must be determined by the general assemblage of the organic remains, and not by a few individuals, or a few species of shells, which differ from the general character of the fossils; particularly as we now know, that several species supposed to be marine, are capable of living in fresh water.

In the great coal formation of England, the upper and middle beds, for many hundred feet or yards in thickness, abound in the remains of terrestrial or of marsh plants with some freshwater shells, but without any admixture of marine species. The whole mass of the coal measures, however, rest on marine limestone; and in some parts of England, the lowest measures alternate with beds of limestone, and also contain some shells supposed to be marine. Though the upper and middle parts of all the English coal fields are freshwater formations, we can have no doubt, that the limestone on which all the coal fields rest was deposited under the ocean; but many circumstances tend to prove, that its elevation was a slow and longcontinued process, and that the lower part of the coal measures was deposited when nearly on a level with the sea, or in situations subject to interruptions of marine water; or else the ground was subject to oscillations, which brought it, at different times, below the level of high tides.

The great valley of the Mississippi contains the largest coal field in the known world; and what is now annually taking place in some parts of that valley, appears to confirm in a remarkable manner, the opinions I have advanced (pages 113 to 118) on the formation of coal and the cause of the frequent recurrence of the same series of strata at different depths, in the same mine; which I attribute to the periodical filling and desiccation of lakes. In the second volume of Mr. Stuart's interesting "Travels in the United States," there is a very instructive account of the Valley of the Mississippi, quoted from an American review. I shall here insert the parts immediately connected with the present subject:

"What is called the Valley of the Mississippi is not in reality a valley, but an extensive elevated plain, without hills or inequalities deserving notice. It extends west from the western slope of the Alleghany Mountains, to the sand plains near the Missouri, a distance of about 1500 miles, and south from the valley of the northern lakes, to the mouth of the Ohio, about 600 miles. No part of the globe possesses such an extent of uniform fertillity. The difference in ele