controvert; and his reasoning on this subject is satisfactory, and enriched with various illustrative facts.

'Enough has been said to make it evident, that neither any single stratum, nor single rock, nor any imaginable series of rocks can be traced in a continuous line round the globe. Similar strata, 'similar rocks, similar series of rocks are, however, found in differ'ent countries and in different hemispheres.-But will this similar'ity of character entitle us to suppose that they were once connect'ed? products of the same æra?" precipitates or deposits from the 'same solvent? Certainly not; for similar rocks are continually seen ' in very different formations. How often do we observe, in a moun'tainous district, recurring strata composed of the same substance, 'separated by a vast thickness of strata composed of other sub'stances!' &c.

'As far as our present experience reaches, granite and gneiss 'seem to belong, peculiarly, though not exclusively, to the more 'ancient rocks: chalk, clay, sand, marle, loam, and rock-salt, to 'the more modern. Gray-wacke, sand-stone, clay-slate, quartzrock, sienite, porphyry, green stone, basalt, serpentine, compact 'feldspar, seem common to both. In general, the younger rocks 'exhibit more abraded fragments than the others, more bituminous ' and saline matter, more organic remains.'

We agree with the author in his opinion respecting fossil organic remains, that, though they may serve to identify strata in a limited district, it is unreasonable to suppose that, if any stratum had ever extended over a large portion of the globe, it would contain the same animals in northern as in southern latitudes. Mr. G. doubts the correctness of many opinions that have been advanced ing organic remains; and he denies that Zoophytes are the first respect'born of animals; for the genealogy of the Nautilus is quite as 'long as that of the Madreporean polypus.' We apprehend, however, that most of those, who have advanced the opinion of the antiquity of Zoophytes, have admitted that many species of Zoophytes and shell-fish were cotemporaneous. We believe it would be difficult to prove that the remains of any vertebrated animals, and particularly of any that were viviparous, ever occur in the secondary strata below the mountain-lime-stone; and we deem the position still correct, that a regular gradation of animals from the more imperfect to the more perfect forms may be traced by their remains, as we ascend from the lower to the uppermost strata: which opinion we do not conceive to be invalidated by any statement that the present author has advanced. The subsequent observations on what are called the Fresh-water-formations are particularly deserving of attention.

'The alternation and occasional intermixture of sea-shells with 'those of fresh water, is common to all the secondary strata, and

not unknown in the transition. The gray-wacke slate of the 'Harz contains encrini and reeds. Sea-shells, accompanied by 'impressions of fern, are observable in the dunstone of Ludlow and South Wales. Coal-shales and nodules of iron-stone, exhibiting 'casts of fresh-water muscles, are often interposed between the co'ralline lime-stones of the northern counties. The monitor, which ' occurs in the copper-slate of Thuringia, is associated with fresh'water fishes and marine shells. The lias affords ferns, nautili, ' and crocodiles; the slate of Stonesfield, remains of birds, beasts, and marine animals. The Petworth and Purbeck marbles, con'taining a species of paludina, alternate with beds of sand-stone, 'charged with marine univalves and bivalves; fruit and leaves are 'found with marine exuviæ in chalk. The clay at Sheppy Island, ' abounding in sea-shells, is reported to yield no less than five hun'dred varieties of fossil fruit; fresh-water shells intermixed with 'marine have been observed, also, at Barton Cliff, at Brentford, ' and other spots near London, in the same bed. The alternation ' of fresh and salt-water productions at Headen in the Isle of Wight, ' and in the corresponding strata of the basin of Paris, is notorious. 'At Guespelle, at Pierre-Laie, at Grignon, &c. sea-shells are in'termixed with fluviatile. At Montmartre the gypsum exhibits 'animals of land, air, and water; the middle beds of that rock con'tain fresh-water shells; the upper and lower, marine.—

'How these extraordinary alternations and intermixtures are to 'be accounted for, and whether they are attributable, in all cases, 'to one and the same cause, it is difficult even to conjecture.

'It should be recollected that many of the opinions here com'bated were advanced at a period when much less was known than 'is known at present, and would now perhaps, if opportunity offer'ed, be disclaimed even by their authors. I make this observation 'not in candour merely, but in prudence; being satisfied that if 'geological science continues to advance at the rate it has done lately, the Essays now submitted to the public will, before many ' years have elapsed, be found to contain as many errors as they 'presume to correct.' Yet we can scarcely perceive any necessity for this apology; since the opinions which the author has advanced as his own are so few and so cautiously guarded, that he can never be convicted of many errors, unless we should call error the constant opposition to every theory that has been advanced by preceding writers. A former president of the Geological Society has well observed that the determination to oppose all system was itself a system, and like other systems had a tendency to obstruct the candid admission of facts and arguments. We entertain much respect for the character and talents of the present author, than whom few persons have had a more extended range of survey, or are better qualified to advance the science of geology by their own ob

servations; and we would beg leave to suggest that one page of accurate observations is worth a whole volume of doubts. With these feelings, we cannot but regret that Mr. Greenough, who now presides over the Geological Society, has so rarely contributed to the volumes which have been published by that body; and the rather because we know not any observer, either in this country or on the Continent, who could more amply enlarge our stock of geological facts, if the dread of falling into errors did not prevent their publication.

[From the Edinburgh Review.—-Jan. 1820.]

On the same Work.

We are partial, perhaps, to this book, from its hostility to that geological dogmatism with which we have been so often offended, and its patronage of that wholesome skepticism to which we have always been so much inclined; and yet, if it had fallen in less happily with our own opinions, we think we should have had the candour to say, that we had never before met with such a treasure of information, and so much bold and free reasoning, in so small a volume, and on such a subject. We have no time at present, to grapple with the author's arguments; and it is extremely difficult to give any continuous abstract, or analysis of statements already so compactly arrayed. But we must endeavour to give our readers some notion of their general tenor, and shall touch on some of the more prominent features of each Essay―referring to the work itself for a great variety of important particulars, and especially for a rich display of illustrations and examples.

ESSAY I. On Stratification.-From a great collection of contradictory passages in the writings of eminent geologists, Mr. G. proves, not only that the stratification of granite, and some other rocks, is a point not yet ascertained; but that some of the main principles connected with the doctrine of stratification in general, are by no means satisfactorily established. Thus, although the parallel planes exhibited by the surfaces of different beds, may frequently have been effected by alternate suspensions and renewals of depositions, yet the same phenomenon is often produced by other causes; as in basaltic pillars, in backs and cutters, in the laminæ of crystals, &c. Besides, the greater or less frequency of the recurrence of parallel planes, depends on the nature of the substances deposited,-granite, porphyry, serpentine trap, salt and chalk, presenting themselves in thick masses, argillite in

flakes, and sand stone and oolite in beds of moderate thickness. The larger divisions of rocks, too, are often not parallel to the laminæ of which they are composed: way-boards, or partings, seem to depend no less on the nature of the adjoining rocks, than on the circumstances which may be supposed to have attended their formation. At the junction of two kinds of rock, we often find a mutual impregnation of their respective substances; the contemporaneous veins of one stratum sometimes penetrates into that which is contiguous to it; and decomposition or torrefaction will frequently reveal stratification which was formerly latent. From all these circumstances, we are warranted to infer, that adjoining strata may, in some instances, be contemporaneous, and that, at all events, stratification is not uniformly the effect of alternate cessations and repetitions of deposition.

Mr. G. shows, in like manner, that a great diversity of opinion obtains, relative to the position of rocks, and that, though vertical planes occur more frequently among those of primitive than among those of secondary character, yet every rock, in different parts of its course, exhibits both the vertical and horizontal position, as is copiously illustrated by examples.

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He then confronts the arguments which have been alleged in favour of the original horizontality of strata, with those which have been urged in support of their original verticality, or, at least, of their high inclination to the horizon; stating, at the same time, with his usual candour, the difficulties which press on the different hypotheses which have been advanced with a view to account for such an inclination. This abstract or summary of the conflicting arguments, is drawn up with great talent and admirable brevity. The curvatures and angularities of mineral masses and strata, with the consideration of their probable causes, likewise pass under his review. It is supposed by Mr. Playfair,' he observes, that the curvature is generally, if not universally, sim'ple, like the superficies of a cylinder, not double, like that of a 'sphere; this is a mistake.-As an instance of curvature extending in both directions, we may mention mantle-shaped strata. This appearance, though it has been most observed in primitive 'rocks, is by no means peculiar to these: in the north of England, 'the limestone mantles round the slate; the coal-measures of Der'byshire mantle round the limestone.-When masses or strata de'cline upon every side towards a certain point, they are said to 'be basin-shaped. Such is the disposition of the mountain lime'stone at Ormeshead, of the coal in South Wales, of the chalk in 'the north of Ireland.-The clam-shell cave at Staffa was proba'bly so named, from the conchoidal form which it derives from 'curvature in the strata.'

In the same spirit, this intrepid reasoner attacks the Huttonian

notion of a horizontal elevation of the strata, while in a flexible and ductile state; and observes, 1. that such a state could have no existence, there being in these substances no intermediate stage between fluidity and consolidation: 2. that the operation of the alleged cause would have given rise to other indications of disturbance, which do not actually appear: 3. that in many cases, no such cause can have operated, as the curved strata rest on horizontal ones, which betray no symptoms of curvature: 4. that even supposing its operation to have taken place, the effects ought to have been very different from actual appearances: 5. that the hypothesis does not account for curvature in horizontal strata: and, lastly, that the conformity of different strata is another circumstance, fatal to this hypothesis.

Regarding the principle of crystallization as alike inadequate to explain the phenomenon of curvature, Mr. Greenough conjectures, that it may depend sometimes on the unequal effect produced by the temperature, on the materials of which the masses are composed, sometimes on the motions of the fluid from which they were deposited, and sometimes on the form of the bottom on which they rest; and the cases to which he alludes, certainly admit of a plausible explanation on one or other of these three principles. In conclusion, he thus puts his brother geologists to the question :Where a rock is stratified, is it necessarily bound by parallel surfaces? if so, let us hear no more of mantle-shaped, saddle-shaped, 'shield-shaped, basin-shaped, trough-shaped stratification.--Are its 'surfaces necessarily parallel to those of the adjoining rock? If so, let us hear no more of unconformable and overlaying stratification. Is it sufficient that parallelism shall be found in a portion of 'the rock? Let us never hear of substances being unstratified? 'Or must it extend through the entire mass? Let us hear no more ' of strata. The lamina of flagstone, the folia of slate, are these ' strata? Are masses of four hundred feet thick, strata? Is there 'any assignable limit to their thickness of tenuity?-When one set of parallel planes crosses another, are both sets to be called strata, or neither, or only one of them? And if one only, by 'what rule are we to be guided in distinguishing the real from 'the counterfeit?-Must the beds be so arranged, as to convey to 'the observer the idea of deposition alternately suspended and renewed? If this is not necessary, how is the parallelism derived 'from stratification, to be distinguished from parallelism resulting 'from other causes? and of what use is it to know whether a sub'stance is stratified or not? If it is necessary, where two observers have imbibed contrary impressions, how shall we determine which ' of the two is right?-Let him who can answer these questions rest 'assured that he has a distinct idea of stratification.'

In geology, as in many other sciences, the loose use of words is