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[From the Monthly Review.-London, Dec. 1819.]

ART. I. A Critical Examination of the First Principles of Geology; in a Series of Essays. By G. B. GREENOUGH, President of the Geological Society, F.R.S. F.L.S. 8vo. pp. 336. London, 1819.

GEOLOGY may date its commencement as a science, from the middle of the last century. Previously to that period, the speculations of philosophers on the formation of the earth, had little connexion with, or reference to existing phenomena, and were, in every respect, as useless and fanciful, as the cosmogonies of the Persians or the Hindoos. Lehman, the German, appears to have been the first to remark, that the different rocks which compose the crust of the globe, admit of a division into two classes; of which the first, or lowermost, are destitute of any imbedded remains of organic life; and the second, which are incumbent on the former, frequently contain the relics of animals or vegetables. To the first he gave the name of primary, on the supposition that they were created previously to the existence of animal or vegetable life on our planet: while to the latter he assigned the name of secondary, supposing that they were for the most part formed from the debris or ruins of the others. This division, which, with certain limitations may still be admitted as correct, may be said to constitute the basis of geology as a science.

Since the time of Lehman, the surface of the globe has been examined with more or less accuracy, in various countries; and an approximation to a certain order of succession has been traced in the rocks which cover the primary, though this order is subject to various irregularities and anomalies, the causes of which remain to be satisfactorily explained. Among the most interesting facts which these investigations have brought to view, may be stated the numerous genera and species of unknown animals which have been buried for countless ages, in the different strata, and which bear a more or less remote resemblance to the present tenants of our planet, but still are distinct from any existing genera or species. The remains of different species of these unknown marine animals, in the various beds that form some of the most elevated parts of the globe, prove, beyond doubt, that our present continents were buried for ages, under the waters of a primæval ocean, and serve to indicate the great changes which the surface of our planet has undergone since the period at which those mountains were

originally formed. In referring to the discoveries of more immediate practical importance, we may remark that coal and various useful minerals are associated with certain rocks, above or below which they never occur in any considerable quantity; and that various metallic minerals have also their peculiar repositories, out of which any search for them would be useless.

We cannot be surprised, that numerous discoveries, so new and interesting, should have given rise to much premature generalization of facts, and to various theories of the earth. Among these, the geology, or, as it was called by its followers, the geognosie, of Werner, was pre-eminently distinguished by the loftiness of its pretensions. It was declared to be a true system of the earth that unfolded the secret causes by which its surface had been successively formed; and, in speaking of Werner, we were told that "this great geognost, after many years of the most laborious investigations, conducted with an accuracy and an acuteness of which we have few examples, discovered the manner in which the crust of the earth is constructed. Having made this great discovery, he, after deep reflection, and in conformity with the strictest rules of deduction, drew most interesting conclusions as to the manner in which the solid mass of the earth may have been formed. It is a splendid specimen of investigation, the most perfect in its kind, ever presented to the world." (Jameson's Mineralogy, vol. i.) Since the period at which this eulogy was written, it has been ascertained, that the system of Werner is nothing more than an attempt to represent the surface of the globe as in perfect accordance with the arrangement and succession of rocks which occur in the vicinity of Saxony, where Werner resided; and it has also been discovered, that he was but an inaccurate observer of the actual arrangement and succession of the rocks around him: or that, misled by an attachment to known theory, he could not, or would not, notice those appearances which were in opposition to his system. With all its errors, the system of Werner had its merit as an approximation to truth, and it was farther useful, as it gave a stimulus to inquiry: numerous observations being made in different countries, by its advocates or its opponents, in order to ascertain its accordance with present appearances, by which our knowledge of the geology of the several districts has been greatly extended.

The remark which we have here made on the utility of Werner's system, may be extended to those of Hutton, De Luc, Whitehurst, and others. It is now, however, generally felt and acknowledged, that facts are the desiderata yet required in the science of geology, and, that the principles at present fully established, are but few in number, though highly interesting and important. By such principles, we mean, the inductions from facts which are ad

mitted by all geologists. Among these inductions may be enumerated, 1st, that all the present continents have at successive epochs been covered by water; 2dly, that the strata which contain the remains of animals or vegetables, were deposited in succession over each other; 3dly, that every stratum containing organic remains, was once the uppermost solid covering of the globe; 4thly, that many of the different species of animals, buried in separate strata, lived and died in the situations in which their remains are now found; 5thly, that the surface of our present continents has undergone successive revolutions, by which the bed of the ocean has been changed; 6thly, at the period of these revolutions, the world was inhabited by genera and species of animals that no longer exist on our planet. These, we believe, may be considered as legitimate deductions from acknowledged facts, received by all geologists; and we are now accustomed to regard them as wellknown truths, which cease to excite surprise, though they would have been viewed with the utmost astonishment, by philosophers, at the beginning of the last century.

As the present volume professes to contain a Critical Examination of the first Principles of Geology, we think that the author ought, at the commencement, to have concisely enumerated what he regarded as first principles; and he might have classed them under four divisions, as certain, probable, dubious, or false. Instead of doing this, Mr. Greenough has presented us with eight essays, in which he has brought forward the conflicting opinion of different geologists, and enumerated facts that are at variance with each of these opinions; which having done, he frequently leaves the reader without any decision on the question at issue. We apprehend, therefore, that those persons who may take up the volume with a view to learn the first principles of geology, will feel more disposed to relinquish than to pursue a science, in which all appears involved in doubt and uncertainty. The design of the work, however, is not so much to teach the first principles of geology, as to show the necessity of a more attentive examination of nature, and to place the evidence of facts above the authority of names, however distinguished. In pursuing this laudable object, Mr. Greenough adduces numerous interesting geological facts, for the knowledge of many of which, we are indebted to his own researches in Great Britain and on the Continent; and these we consider as constituting the principal value of the publication. **

'Stratum (Mr. G. observes) is a word so familiar to our ears, 'that it requires some degree of manliness to acknowledge our'selves ignorant of its meaning: the sense in which it is used is however very far from being precise. Easy as it may seem to de'termine whether a given mass be or be not stratified, there is per'haps in the whole range of geological investigation no subject

'more pregnant with controversy.' (P. 1.)-Stratum is a literal 'translation of the word bed, and most writers use one or other of 'these expressions indifferently. Professor Jameson, not con'sidering how injudicious it is to employ synonymes for the pur'pose of expressing contrast, has introduced a distinction between 'them. Similar contiguous masses are by him denominated strata, 'dissimilar ones beds. Mr. Martin has protested against this inno'vation, and few authors without the Wernerian pale appear dis'posed to adopt it. Those who feel the value of such a distinction would do well therefore to select some happier phrase to express 'it.' (P. 9.)

It has been supposed, without sufficient evidence, that stratification necessarily implies a formation by aqueous deposition, in the manner in which mud or sand is spread at the bottom of lakes or on the shores of the ocean: but volcanic rocks are sometimes regularly stratified: not only those which have been formed by showers of dust and scoriæ, but those which have flowed as melted lava. The tendency to split into parallel layers appears frequently to result from an imperfect kind of crystallization in the mass, and takes place in various rocks, particularly when exposed to atmospheric influence. The geologists who have been attached to the aqueous theory have denominated these parallel layers strata but those who have adopted the Plutonian theory have refused to admit the stratification of such rocks. According to Mr. Greenough, this contrariety of opinion is caused by the indefinite application of the word stratum: 'every one uses the word, but no one 'inquires its meaning: the remedy is obvious, definition.'-As the remedy for this evil appears so obvious to the President of the Geological Society, we entertained the hope that he would have rescued the science from farther confusion and obscurity on this important subject, by giving his own definition of stratification: but we sought for such a definition in vain. Indeed, from the summary at the conclusion, we are rather led to infer that the word stratification is destitute of any precise meaning, and is utterly undefinable. ***

The continental geologists say that Mr. Greenough has quoted indiscriminately foreign writers of very unequal merit; and that he has given the opinions of authors who wrote early in the last century, when little was known of geology, as possessing the same value as the observations of the most accurate of modern geologists. We confess that there is much truth in this remark, which we have frequently heard on the Continent when Mr. G.'s book has been the subject of conversation; and the President himself; who indulges so often in a smile at the contradiction or supposed ignorance of preceding writers, will not be surprised to find that his brethren on the other side of the water are also disposed to en

courage les sourirs un peu malins when his own errors are discovered and criticised. They are wrong, however, in the inference "ex capite corporem," as applied to the President of an English Society.

In Essay the third, Mr. G. seems disposed to admit that, previously to the great deluge mentioned in the second Essay, a deluge similar in kind had occurred, though perhaps not equal in extent to that which determined the present outline of the earth. He founds this opinion on the almost universal occurrence of conglo'merate and gray-wacke on the confines of what are called primi'tive rocks.' It may, however, be fairly asked how this conglomerate escaped being swept away by the second deluge? To volcanoes and earthquakes, Mr. G. seems disposed to allow a very limited range of action. He states that it is not probable that the deluge was effected by a cause residing within the earth :— for, he says, 'we are not aware of any force depending on 'the internal constitution of the earth, that could effect so 'great a revolution as the deluge:'-but are we to deny that the earthquake which destroyed Lisbon, in the middle of the last century, was produced by a force residing within the earth? That earthquake shook at the same time all Europe, a great part if not the whole of Africa, the continent of North America, and the West-India islands, and produced a violent agitation of the whole Atlantic Ocean. We say, then, are we to deny that this vast commotion of the surface of the globe was produced by a force residing within it, because we are not aware of any force depending on the internal constitution of our planet which could produce so mighty an effect? As well might we deny the emission of light from the sun, because we are not aware of any force in the internal constitution of that orb which can propel the particles of light with such astonishing velocity. On this subject, the Plutonist has greatly the advantage of the cometist; for he refers to a cause which, though he cannot explain it, is known to exist, and to be constantly operative: he can appeal to the evidence of his senses and of history, to show that many hundreds and even thousands of square miles of the earth's surface have been overwhelmed or disturbed by the same cause.

On Formations. By this term, the author observes, is meant a 'series of rocks supposed to have been formed in the same manner 'and at the same period. The idea is therefore purely theoretical.' It has been asserted by Werner that the greater number of rocks are universal formations; or, in other words, that each different order, as granite, gneiss, mica-slate, &c. is spread universally over the earth's surface, like the coat of an onion, and that the same rocks in distant regions were cotemporaneous. These positions, Mr. G., in common with many modern geologists, is disposed to VOL. I.

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