perhaps, of the more ancient classes of rocks. But, in addition to the customary occupations of his calling, his work bears proof of indefatigable activity in collecting information from quarters apparently very remote from his immediate pursuits; and it has. been justly remarked, that he possesses powers of assimilation,'* which enable him to convert the most heterogeneous and unpromising materials into good wholesome geology.

The first volume of the author's Principles' was published in 1830-the third and concluding volume, in 1833. In 1834, the work was honoured by the Royal Society with one of the Royal medals for that year; and its reception by the public is best evinced by the fact, that four new editions had been called for between its first appearance and the summer of 1838.

One of the chief defects, in our judgment, of this remarkable performance is, that it is perhaps too much lowered to the popular appetite-and wants, in many places, that severity and closeness, both of reasoning and style, which are called for by the rapid expansion of the subject, and by the relations, every day multiplied, between geology and the higher departments of natural science. The book, at first, appeared to us to be the production of an advocate, deeply impressed with the dignity and truth of his cause. The tone was rather that of eloquent pleading than of strict philosophical enquiry; and though, in the later editions, this defect is much less prominent, the author does not yet appear to have been sufficiently careful in distinguishing what has been proved from what is only probable—the known from the doubtful. Speculation is his great delight, and is too often indulged in. He takes up a new conjecture with evident enjoyment; and sometimes leads his readers through a series of possibilities very happily expressed, till those who are desirous of real knowledge are disappointed by finding, at the end of the train, that they have been made acquainted with something which may, or may not, be true.

The management of quotations and references is attended with some difficulty in every work which combines discovery with compilation. In such a volume as the 'Elements,' frequent references were impracticable; and the author's contemporaries, certainly, have here nothing to complain of. But in his larger work-preceded by a general history, and passing through all the departments of geological research-much attention was called for upon this point; and we have seen with pleasure that increased care seems to have been devoted to it in the successive editions.

* Conybeare's Report to Brit. Assoc, Vol. I., p. 406.

The best mode of performing the duty of reference, and we should imagine the most comfortable to an author himself, would be to act always under the impression that he is invested with the functions of a judge, and engaged in dispensing the highest honour that can be awarded to the cultivators of science; for, if the appreciation of their works by fellow-labourers be denied to authors, we really know not, after all that has been said on this subject, where their external reward is to be found. With respect to information casually obtained in society, or in conversation, it must be still more difficult to connect new facts or observations with their authority. But here, also, it is a duty to do all one can, to guard against the natural tendency to silent approbation; while on the other hand, those who give information, or suggest hints of enquiry, should recollect that it is frequently the application to his own subject, made by the writer himself, and not the mere substance of the communication, that constitutes its value.

A defect, or rather omission, connected with what we have just mentioned, is perhaps rendered more important in our eyes by some early associations. We think that Mr Lyell has not, either in his preliminary history or in the body of his works, done quite sufficient justice to the claims of DR HUTTON-Whom we conceive to be effectively the author of the Theory of the Earth now almost universally received;-and that in adopting the metamorphic theory, and the views connected with it, by modern writers, he ought to have referred more emphatically to the works of that very remarkable man, as the source from which those doctrines were first obtained. This defective appreciation of Hutton, we have no doubt, may be ascribed, in a great measure, to the direction given by accidental causes to Mr Lyell's own pursuits; but it is the more unfortunate, as the public and the general reader will naturally make a work so popular as the Principles of Geology' their text-book and authority; while many eminent men, engaged in the cultivation of other departments of physical science, will be content to take their impression from the clear and fluent pages of that publication; with some indifference, perhaps, as to the relative merit of those by whom geology has been advanced to its present state. We could show, by some striking instances, that this is no imaginary

case.

To supply this omission, and, as far as we can, restore to its proper station what appears to us to be the truth, we shall not hesitate, before the close of the present article, to call the attention of our readers to the progress of the subject during the fifty

years which have elapsed since the publication of Dr Hutton's Theory of the Earth.' But we must first lay before them an analysis of the volume immediately before us, which will enable them to judge the better of what we shall then subjoin.

'Of what materials is the earth composed; and in what manner are those materials arranged?-These are the enquiries with which geology* is occupied.' We are glad to find, in this first sentence of his work, a somewhat different view of the subject from that taken at the commencement of his 'Principles,'— where geology is described as the science which investigates the 'successive changes which have taken place in the organic and ' inorganic kingdoms of nature.' The latter definition [seems to throw into the shade all that relates to the permanent or average condition of the globe; which is in itself a very important subject of study.

The volume is divided into two nearly equal parts, containing respectively the answers to the questions above mentioned :—the first part describing the materials composing the exterior of the earth; the second, recounting the different ages of the stratified and massive rocks, in the order of the successive periods when they appear to have been deposited or produced from below.

Rocks,' therefore, (a term which in its geological sense includes not only the harder stony masses, but also clay and sand, &c.,) may be studied under two distinct points of view :-simply as ' mineral masses, originating from particular causes, and having ' each a certain composition and character; or as a chronological 'series of monuments, attesting a succession of events in the former history of the globe.' The classes into which they are divided by Mr Lyell, are four: 1. Aqueous-sedimentary, or fossiliferous. 2. Volcanic 3. Plutonic. 4. Metamorphic. The last three divisions are very intimately allied; the fourth being, in fact, no more than a portion of the sedimentary strata changed by Plutonic agency. Pluto, it is well known, presides over the internal, deep-seated regions of the globe, where the operations of fire originate; while Vulcan is the workman who manufactures the lavas, scoriæ, and ashes, sent out upon the surface.

The author, in the successive chapters of his first division,

* De Luc, in 1778, calls his Letters to the Queen of England, the outline of a Treatise on Cosmology;' intending by that term to signify la connaissance de la Terre, et non celle de l'Univers. Dans ce sens,' he adds, Géologie eût été le mot propre; mais je n'ose m'en servir parcequ'il n'est pas usité.'-Lett. Physiques Svo, 1778; Préface, pp. vii. viii.

treats of the general composition and structure of these classes; and in the second goes through the several groups which form the series of rocks, in a descending order, from the newest to the most ancient.

The mode in which the sedimentary rocks have been produced, is well illustrated in the following passage; the lines printed in Italics, expressing the principle by which the continuity or identity of the deposit in a lake is recognised; and the means also by which geologists are enabled to trace the stratification of countries through much more extensive regions:

'If we drain a lake which has been fed by a small stream, we frequently find at the bottom a series of deposits, disposed with considerable regularity, one above the other: the uppermost, perhaps, may be a stratum of peat; next below, a more dense and solid variety of the same material; still lower, a bed of laminated shell marl, alternating with peat or sand; and then other beds of marl, divided by layers of clay. Now, if a second pit be sunk through the same continuous lacustrine formation, at some distance from the first, we commonly meet with nearly the same series of beds—yet with slight variations; some, for example, of the layers of sand, clay, or marl, may be wanting-one or more of them having thinned out and given place to others; or sometimes one of the masses first examined is observed to increase in thickness to the exclusion of other beds. It will be seen in the sequel, that many distinct sets of sedimentary strata, each several hundreds or thousands of feet thick, are piled, one upon the other, in the earth's crust, each containing their peculiar fossil animals and plants; which are distinguishable, with few exceptions, from species now living.'Pp. 5-10.

The Plutonic class comprehends the granites, porphyries, and other massive rocks: their texture is crystalline, and they are entirely destitute of organic remains. It is admitted that nothing analogous to these can be seen in process of formation on the actual surface of the earth; but the proofs of their igneous origin comprehend some of the most extraordinary facts which geology has brought into view; and they are said to be connected, by a series of transitions, with the products of actual volcanoes.

The mode of formation in the 'Metamorphic Rocks,' (gneiss, mica-schist, clay-slate, &c.,) is less certain than that of the other classes. They contain no pebbles, sand, or scoriæ; and no traces, or very rarely, of organic bodies; yet they are divided into beds analogous to those of sedimentary deposits. Respecting this curious class of strata, Mr Lyell has adopted the theory, of which Hutton had announced the fundamental doctrines nearly fifty years ago;-long before many of the phenomena were discovered by which his views have been since illustrated and confirmed. The abode of the strata thus metamorphosed' in the regions of

internal heat, or their proximity to great plutonie masses in a state of fusion, seems to have been the chief cause of their change. But how far electricity, or any other agents, have co-operated with heat in producing it, is still matter of speculation.

The relations of these four classes are illustrated in this volume by a coloured plate, analogous to the large and beautiful section of Mr Webster, published in Dr Buckland's Bridgewater Treatise,'-which, by an ingenious addition, explains how the several classes of rocks may have been produced contemporaneously. We regret that we cannot adopt this plate, as it requires the aid of colour: but we insert a wood-cut, in which the relative position of the plutonic and sedimentary series is exhibited; and it is shown that, while the order of super-position indicates the date of the latter groups, the newer plutonic masses are successively lower, or deeper seated, than the rest.

Here, while the aqueous deposits, 4, (which we suppose to be the most recent of the sedimentary series 1, 2, 3, 4,) are in progress of accumulation, we may conceive a plutonic mass in igneous fusion; IV. to be forced up from below, through the incumbent matter, 'invading' (to use the phrase of Dr Hutton) all the strata then existing above it ;-as similar plutonic masses of former epochs, I. II. III., had previously done. In each case, a ('metamorphic') change would be produced, by the proximity of the heated masses in the adjacent portions of the strata which they traverse. This effect we have endeavoured to represent by a slight shade; the continuation of which, in 2, is intended to indicate that the metamorphic character is not confined to one division—but that all, or any of the sedimentary strata, whether secondary or tertiary, may be thus altered.