period disappeared, and other and different races were introduced before the deposition of the clay. And how different the clay itself from the chalk; and what a different combination of circumstances must have been required for its deposition! This abrupt transition from the chalk formation to the next succeeding, is recognized in numerous localities in the different quarters of the globe, and appears to have been absolutely universal. Other similar abrupt transitions between contiguous formations in lower and older strata are well known; but unfortunately for this hypothesis, the exact number of six cannot be made out.

At another time the notion prevailed very extensively that most or all the changes that have taken place in the crust of the globe, as indicated by its rocky strata, may have been produced by the flood of Noah, and its attendant circumstances.

It is scarcely necessary so say that these opinions have now at length been discarded almost universally, and geologists of all countries agree in the opinion that we are to look for the causes of all the changes the crust of this globe has undergone, only to the same geological agents as we know now to be constantly at work. Some of them, from the nature of the case, were probably more active in the early geological periods than they now are, but in other respects they are the same. Hutton indeed has the credit of having given expression to this opinion at a comparatively early period, but for a long time it gained few adherents. His work, entitled "Theory of the Earth," in which the opinion is expressed, was published in 1788;* but it was reserved for Lyell, more than forty years later, to search out and give to the world the convincing proofs of this doctrine. His great work, entitled "Principles of Geology, being an Inquiry how far the Former Changes of the Earth's Surface are Referrible to Causes now in Operation," which made its appearance in 1830, though at first violently opposed by some very good men, gradually won its way to the confidence of candid inquirers, and became the chief agent in forming the present universal belief on this subject.

This work of Lyell is a prodigy of its kind; and though *Lyell's Principles, vol. i, pp. 69, 71, Phil. Ed.

treating of a science which is making constant, and almost daily progress, it can never become obsolete. With singular industry the author ransacked the whole range of ancient and modern literature for recorded instances to prove and illustrate the great geological changes that have occurred during the period covered by the history of our race; and also visited a greater number of important geological localities, thus probably extending his own personal observations over a larger portion of the earth's surface than any other professed geologist has ever done. The book is written in an easy, perspicuous style; and what is more, every page evinces the perfect sincerity and candor with which every fact is stated, and every opinion expressed.

But did Lyell himself fully appreciate the deep importance and extended bearing of his own teachings?

This doctrine, that the earth's surface or crust has come to its present condition by the slow operation of natural agents, even the same as we now see at work, makes the science of geology-at least in one of its principal departments-simply a history; and, as a matter of course, it requires to be treated as such. On this view there has been in all past time, from the earliest periods, a regular succession of events in the operation of the various geological agencies; the condition of things in the earth's crust at any time being not only the result of causes still in operation, but at the same time also growing out of the condition of things in the age next preceding. Thus the condition of things at the present age, in any place, must have grown out of that of the last age, and the condition of things in the last age must have grown out of that in the next preceding, and so on indefinitely. It is indeed true, if the crust of the earth has been brought to its present condition, not by the operation of natural causes, but by a succession of miracles, it still has a history, in a sense, but then this history must be limited to a mere description of the successive cataclysms; and these being, as supposed, mere arbitrary interferences of divine power, there would not necessarily be any connection between them. And so too, if the present condition of the earth be the result of the action of geological agents, but modified by occasional miraculous interferences, there can be no longer any

reasoning from effect to cause, since we never can be certain, in regard to any particular thing, whether it be the effect of the cause supposed, or whether it be not, on the other hand, the result solely of miraculous agency.

But after illustrating and proving, in so able a manner, the truth of Hutton's early but sagacious view, which as we have seen makes the science of geology a history, how does Lyell proceed to present this history before us? Why, "back end foremost," beginning by describing first the most recent events, and closing with the most ancient!* But this work of Lyell, though really a history written backwards, has for more than thirty years maintained the position it took very soon after its publication, as a standard authority, not indeed inferior to any other in any language!

At length, however, in this excellent work of Prof. Dana, we have the true idea realized: a history of the earth written in the order of the events. And if the publication of Lyell's work, a third of a century ago, marked an era in the progress of opinions on this branch of science, so will this also, but in a different way. It may not indeed effect such a change of opinion on any important point connected with the science, but it invests American geology, at least, with such new interest, and throws around the study of it such new charms, that we may reasonably expect it to receive a new impulse.

But while geology is properly a history, we are not to understand that historical geology is the whole of the science. There are other departments besides the historical, of which we shall have occasion to speak subsequently.

*"It has been often said that geology is a history, the records of which are written in the rocks; and such is its highest department. But is this clearly appreciated? If so, why do we find text-books, even the one highest in authority in the English language, written back end foremost, like a history of England commencing with the reign of Victoria? In history the phases of every age are deeply rooted in the preceding, and intimately dependent on the whole past. There is a literal unfolding of events as time moves on; and this is eminently true of geology."—Dana's Address at Providence. Proceedings of the American Association for the Advancement of Science; Ninth Meeting, held at Providence, R. I., August, 1855, p. 4.

One or two small works on geology have heretofore been published, which treat the subject in this order, but no one, it is believed, which is of standard authority.

We have already more than intimated our opinion of this work; we consider it not inferior to any other in the language, and, for American students especially, vastly superior to all others. The very beginning, the "Introduction," is surpassingly beautiful, and the reading of it cannot fail deeply to impress the mind, and prepare it for the eloquent pages that are to follow.

1. Kingdoms of Nature. Science, in her survey of the earth, has recognized three kingdoms of nature: the animal, the vegetable, and the inorganic; or, naming them from the forms characteristic of each, the Animal Kingdom, the Plant Kingdom, and the Crystal Kingdom. An individual in either kingdom has its systematic mode of formation and growth.-P. 1.

The particular mode of growth of the individual in each kingdom being then described, substantially as by other writers, the author proceeds:

2. But the earth, also, according to geology, has been brought to its present condition through a series of changes or progressive formations, and from a state as utterly featureless as a germ. Moreover, like a plant or animal, it has its special systems of interior and exterior structure, and of interior and exterior conditions, movements, and changes; and although Infinite Mind has guided all events toward the great end, a world of mind, the earth has, under this guidance and appointed law, passed through a reg ular course of history and growth. Having therefore, as a sphere, its comprehensive system of growth, it is a unit or individual, not indeed in either of the three kingdoms of nature which have been mentioned, but in a higher, a world kingdom. Every sphere in space must have had a related system of growth, and all are, in fact, individuals of this kingdom of worlds.

Geology treats of the earth in this grand relation. . .

3. The earth, regarded as an individuality in a world-kingdom, has not only its comprehensive system of growth, in which strata have been added to strata, continents and seas defined, mountains reared, and valleys, rivers, and plains formed, all in orderly plan, but also a system of currents in its oceans and atmosphere, the earth's circulating system; its equally world-wide system in the distribution of heat, light, moisture, and magnetism; plants and animals; its system of secular variations (daily, annual, etc.,) in its climate and all meteorological phenomena. In these characteristics the sphere before us is an individual, as much as a crystal or a tree; and, to arrive at any correct views on these subjects, the world must be regarded in this capacity. The distribution of man and nations, and of all productions that pertain to man's welfare, comes in under the same grand relation; for in helping to carry forward man's progress as a race, the sphere is working out its final purpose. Pp. 1 and 2.

Geology then takes its proper place as a distinct branch of the science of nature or natural history. It is not a dull discussion of cataclysms and convulsions that have occurred in the earth in past times without law or order, with descriptions of disgusting monsters, "hobgoblins and chimeras dire," but a grand development of events which have taken place in regular order, those of any one period having had their origin and cause in those of the next preceding, and so on in long succession; all this, of course, under the control and continued superintendence of the same Divine Mind that in infinite wisdom. originally called matter into being, and gave it its properties and laws.

But before entering upon the discussion of the earth's individual development, it will add much to the interest of the study if we understand the true "relation of the earth to the universe." This topic the author of this work briefly but beautifully places before us as follows:

Relation of the Earth to the Universe. While recognizing the earth as a sphere in a world-kingdom, it is also important to observe that the earth holds a very subordinate position in the system of the heavens. It is one of the smaller satellites of the sun; its size about 1.400.000 that of the sun. And the planetary system to which it belongs, although three thousand millions of miles in radius, is but one among myriads, the nearest star [being] seven thousand times further off than Neptune. Thus it appears that the earth is a very little object in the universe. Hence we naturally conclude that the earth is but a dependent part of the solar system; that as a satellite of the sun, in conjunction with other planets, it could no more have existed before the sun, or our planetary system before the universe of which it is a part, than the hand before the body which it obediently attends.

Truly insignificant and unimportant this our earthly footstool is, considered comparatively in this light, but not so insignificant or unimportant when considered in another light. The author proceeds:

Although thus diminutive, the laws of the earth are the laws of the universe. One of the fundamental laws of matter is gravitation; and this we trace not only through our planetary system, but among the fixed stars, and thus know that one law pervades the universe.

The rays of light which come in from the remote limits of space are a visible declaration of unity. . .

Meteoric stones are specimens of celestial bodies occasionally sent to us from the heavens. They exemplify the same chemical