of the earth, are caries or abscesses of the mineral kingdom, and the metals themselves are the products of decay and disease, and hence the offensive odor of some of these products.

These several theories, and a great variety of others have been invented in order to account for the same phenomena, and to solve the same problem, viz. in what manner or by what changes, or events, are we to account for the present appearances, or condition of the earth's surface? The reader will observe in general, that these theorists, instead of taking the trouble to observe facts and to draw just conclusions from them, have in the first place formed their systems, and supported them in the best manner they could, calling to their aid, ingenuity, plausibility, and false argument.

The science of Geology never progressed, until men saw the folly of forming theories which had no concern with facts. To record facts is the first business of the geologist, and if he cannot account for them in a rational and scientific manner, to let them stand recorded until further investigations.

Plutonian and Neptunian Doctrines. We shall close this part of our volume by an abstract of the theories of Werner and Hutton, commonly entitled the Neptunian and Plutonian doctrines.

The theories of these two distinguished philosophers for the last half century, have divided the opinions of geological writers, each side insisting in the most positive and uncompromising terms, on the truth of their adopted

cause.

The Plutonians or Hultonians, attribute most of the present appearances of the globe, and the changes it has undergone to the agency of fire, not, however, entirely rejecting that of water.

The Neptunians or Wernerians on the contrary, affect to prove in as positive terms that these same changes, and appearances may, with the exception of volcanic products, be traced entirely to the agency of water—“ to aqueous solution, disintegration, and deposition.

There is one difficulty in attempting to expound the doctrines of Werner, which is, that we are obliged to take them second handed, from the writings of others, he having never himself published them in a connected view. In

speaking therefore of Werner's theory, we can only avail ourselves of such transient glimpses as he has himself thought fit to give us, and must fill up the various chasms with materials derived from the more extended sketches and illustrations of his pupils.*

Werner's theory may be thus stated. The matter of our globe was once in a soft, or semi-fluid state, or at least its nucleus was once enveloped by a chaotic aqueous solution, of such a nature as to retain the various earthy bodies found in the lowest strata in chemical combination; but this state of things was of short duration, and during which, there was deposited from the water a variety of crystalline aggregates, such as the different species of granite, and what are called primitive slate, and primitive limestones. These constitute the primary rocks, or formations of the Wernerian school, and are supposed to have had their origin before the creation of animated beings, and hence no organic remains, such as shells, are found in these rocks. The second class of rocks are supposed to have been formed during the transition of the earth from its chaotic, to its habitable state, and hence are called transition rocks. These are partly crystalline aggregates, and partly mechanical deposites from water: they contain the fragments of pre-existing rocks cemented together, and sometimes contain imperfect remains of the lower orders of animals and plants, as shells and impressions of ferns. Certain kinds of limestone and sandstones belong to this class. These rocks are derived from the fragmentary remains and the disintegration of the primitive rocks.

The third class of rocks are supposed to have been formed by the action of the natural elements on these, and by which they have been broken down, and mechanically diffused in water. The action of frost, water, and attrition are supposed to have chiefly produced this effect, after which the materials were deposited in horizontal strata. These are the Floetz, or flat rocks of Werner, and the Tertiary, or secondary rocks of later authors. They abound in vegetable and animal remains, as ferns, shells, fish, and bones. The newer limestone, red sandstone, and coal strata, belong to this clsss.

* Brand's Outlines of Geology, p. 21

Above these rocks we find depositions of sand, and gravel, and clay; accumulations of peat, and other substances now in the progress of deposition, and which are included under the general term of alluvial formations. These constitute the fourth class. The fifth class contains the products of volcanoes, whether the result of fusion or not, such as rocks thrown out without melting, volcanic mud, &c.

It is supposed that all the formations as they are termed, or all the different kinds of rocks and strata now found on the earth, will fall under one or another of these classes. But it will be seen hereafter, that this theory is, in many respects, unsatisfactory, and that there are several rocks, such as basalt and greenstone, which certainly are not of aqueous origin, and which do not come within Werner's volcanic class.

Werner was appointed professor of mineralogy, at the school of Mines, in Saxony, in 1775, and was undoubtely a man of the highest order of talents. His mind was at once sound, imaginative, and richly stored with miscellaneous knowledge. He had a great aversion to the mechanical labor of writing, and could never be persuaded to pen more than a few brief sketches, and which never contained a connected developement of his geological views. Although the natural modesty of his disposition was excessive, approaching even timidity, yet he indulged in the most bold and sweeping generalization, and he inspired all his pupils, some of which became writers of great eminence, with the most implicit faith in his doctrines.

"Their admiration," says Mr. Lyell," of his genius, and the feelings of gratitude and friendship which they all felt for him, were not undeserved; but the supreme authority which he usurped over his contemporaries, was probably in the event prejudicial to the progress of science.

The Plutonic, or Huttonian Theory owes its origin to Dr. Hutton, of Edinburgh. It was published in 1788, but has been more recently illustrated and defended in a republication by Professor Playfair, also of Edinburgh.

We have already stated that the Plutonians attributed the same phenomena to fire, which the Neptunians did to water. The Plutonians, however, suppose that most straified rocks were deposited from water.

Hutton's Theory may be stated shortly, as follows.The materials which compose the present surface of the

globe, have been derived from the ruin of ancient rocks, which have been disintegrated and pulverized by the continued action of torrents and currents of water; and by the same means these materials have been transported to the bottom of the ocean. Here they have been consolidated, partly by time, and partly by the pressure of the water, but chiefly by the effects of subterranean heat. By the same cause, more powerfully exerted, that is, by the expansive power of volcanic heat, the strata thus formed, have been elevated from the bottom of the ocean, to occupy the situ ations under which they now appear. Thus the strata are thrown into different degrees of inclination to the horizon; or are broken and dislocated; or appear in nearly a vertical position, depending on the degree of force, or the point of its application. Sometimes, also, where the heat has been most intense, an entire fusion of the materials has been effected. The rocks which are not stratified, or not composed of layers, as granite, are supposed to have undergone complete fusion, while those which consist of layers, as mica slate, are supposed only to have been softened by the heat. The same disintegration, and corrosion, and the same transportation to the sea, is constantly going on with respect to the present rocks, so that finally these materials will again be restored to the sea, to be again raised above its surface by volcanic fire, as before; and as the present continents were formed by the destruction of ancient rocks, so future continents will be formed in their turn, by rocks now preparing for that purpose.

It is generally acknowledged at the present day, that Hutton's theory will account for a much greater number of geological phenomena than Werner's. It is impossible, for instance, to account for the present situation of stratified rocks containing sea shells, unless we suppose, either that the sea occupied the earth for ages, or that these strata were formed under the ocean, and elevated by some mighty force; and as we know that islands are thrown up from the sea, by volcanic force at the present day, it is reasonable to attribute the same effect to the same cause, anciently.

GENERAL FORM AND CONSTITUTION OF THE GLOBE.

Although in a popular sense the form of the earth is that of a globe, yet science has long since determined, that its figure is not that of a perfect sphere, but of an oblate spheroid, the diameter at the equator being greater than at the poles. This difference has been variously estimated, but if we consider the polar, to the equitorial diameter in the proportion of 304 to 305, we shall perhaps come as near the truth as the present state of observations will warrant. This allows the poles a compression equal to 1-305, and the two diameters as follows. Equitorial diameter, about The Polar diameter

7,924 miles.

7,898 miles.

This estimate is from the authority of Daubuisson. Dr. Macculloch makes the difference somewhat greater, but we need not here go into comparisons on a point where no two authors agree, the difference of a few miles being a matter of no consequence to our present purpose.

This form of the earth is precisely such an one as it would have taken had it been a homogenous semi-fluid with a rapid motion around its axis. This form may be illustrated by fixing a ball of soft clay on a spindle and setting it in motion. The ball will be flattened at the poles or axis of motion, and elongated or thrown out, at the circumference, or equator. This is obviously the consequence of the greater centrifugal force at the circumference than at the centre of motion.

Density of the Earth. It has been attempted to estimate the density of the whole earth from that of a particular mountain. For this purpose Dr. Maskelyne made an experiment on mount Schihallien, a high precipitous cliff in Scotland, in order to ascertain the force of its attraction, on a suspended plummet; with the view of deducing the density of the whole earth by comparing its