sea plants were of more ancient origin than land plants. A careful study of the genera and species of petrifactions, disclo sed to him another important fact, viz. that the petrifactions contained in the oldest rocks are very different from any of the species of the present time; that the newer the formation, the more do the remains approach in form to the organic beings of the present creation; and that, in the very newest formations, fossil remains of the presently existing species occur. He also ascertained, that the petrifactions in the oldest rocks are much more mineralized than those in the newer rocks, and that in the newest rocks they are merely bleached or calcined. He found that some species of petrifactions were confined to particular beds, others were distributed throughout the whole formations, and others seem to occur in several different formations; the original species found in these formations appearing to have been so constituted, as to live through a variety of changes, which has destroyed hundreds of other species, which we find confined to particular beds.

3. Werner's Advice to Students of Geology.

The following observations, addressed to students of geology by Werner, as given by Daubuisson in his excellent System of Geology, will be read with interest.

I would, in the first place, he says, remind them, that there are various branches of physical science with which they must be acquainted.

In the first rank we would place Mineralogy (Oryctognosy), the department of natural history which makes us acquainted with simple minerals, and enables us to distinguish them from each other. All the observations of the geologist who is unacquainted with it are imperfect, and generally of but little value. When he would ascertain the constitution of a formation (térrain), and such is almost always his object, he must first indicate the mineral substances which enter into its constitution, and then describe the manner in which they are disposed. Mineralogy can alone enable him to execute the first; and it is only when it has been accomplished that he can properly pass to the second. How many estimable naturalists have unprofitably wasted their time and their labour, from having engaged

in geognostical undertakings without a sufficient knowledge of mineralogy! The book of nature, they said, was open to them; but it was necessary to know the characters in which that book is written, and these characters are, in this case, the simple minerals.

It is sufficient to bear in mind that natural philosophy makes known the laws which seem to regulate matter; and especially, that, having the phenomena of nature, and the causes which produce them, continually before our eyes, it enables us to seize and appreciate the relations which may exist between effects which we see, and the causes to which we are led to attribute them, to show how necessary this science is to geology, which occupies itself with the revolutions of the terrestrial globe, and which endeavours to account for the changes which its surface undergoes, or may have undergone.

When this same observer enters into the details of the formation of minerals, he sees nothing but precipitations, crystallizations, and solutions: the forces which have produced minerals, which have collected and united their elements, are forces of affinity; he cannot duly appreciate their effects, without a profound knowledge of general chemistry. But it is necessary for him to employ much reserve and much discernment when, from what takes place in our laboratories, he would draw inferences respecting what takes place in those of nature. Nature acts on immense masses; she has time at her disposal, it is nothing to her; and these two circumstances often suffice to render entirely dissimilar the effects of the same agent and the products of the same cause. Besides we cannot flatter ourselves with possessing a knowledge of all the means which nature employs in her formations, nor can we conclude that she cannot produce a particular effect, because we have not yet been able to imitate it in our laboratories; for example, that a substance is indecomposable, because we have not yet been able to decompose it.

The other branches of natural history, zoology and botany, are also of great utility to the geologist. They make known to him that multiplicity of corals, and shells, those remains of other animals, and also of vegetables, which he finds so abundantly in many of the strata of the globe, and which throw so much light upon the different epochs, and upon many other circumstances,

of formation. A person ignorant of this kind of knowledge being always obliged to have recourse to other naturalists, would be interrupted at every step in the study of secondary, tertiary and alluvial deposites.

Besides the various acquirements which we have already enumerated, the geologist ought to possess a mind capable of comprehending not only those extensive relations that exist in the mineral kingdom, but also its minuter details. Placed in some measure between the astronomer, who carries his observations into the immensity of space, and rises to the infinitely great, and the scrupulous naturalist, who, armed with a microscope, endeavours to discover the secrets of nature in the organs of a mite, or the laminæ of a small crystal; with the grand and extensive views of the one, he must combine the sagacity and accuracy of the other.

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Furnished with the necessary knowledge, and endowed with the requisite qualities, he who is desirous of prosecuting the study of geology, ought to take Nature as his principal conductor. It is only by examining minerals in their native bed that he can be led to rational ideas respecting their formation; it is only by seeing the beds and veins with his own eyes that he can acquire an accurate knowledge of their form, structure, and mutual arrangement; it is only after he has seen and observed much for himself, that he will be able to appreciate the observations of others, submit them to just criticism, and draw inferences from them. It is to him especially that the first lesson applies, which Wallerius gave to his pupils in mineralogy, when he recommended to them to go, on foot, and hammer in hand, to study and interrogate Nature in her own workshops. "Ite filii," says he, “emite calceos; montes accedite; valles, solitudines, littora maris, terræ profundos, sinus inquirite; mineralium ordines, proprietates, nascendi modus notate: tandem carbones emite, fornaces construite, et sine tædio coquite; ita enim ad corporum proprietatumque cognitionem pervenietis ; alias non*." It is not so much the number as the accuracy of the observations that is of importance; and here unfortunately observers have too often to struggle against the inclination natural to all

Systema Mineralogicum, Præfatio.

APRIL-JUNE 1829.

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men desirous of instruction. When, on traversing a country, they have acquired a general idea of its nature, and wish to go farther, it is with difficulty that they can persuade themselves to retrace their steps, to see and see over again the same object under all its aspects, and in all its details; and yet these are the observations that are truly useful to science, those which assure its progress, and which it carefully preserves in its archives. Let the geologist who would make such observations, undertake, for example, the complete description of a country, interesting from its mineralogical nature, but of small extent. Let him acquire

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a first idea of the ground, by traversing it in two or three dif ferent directions, so that he may be enabled to form a right plan of the labour to be executed, and determine the series of questions to be solved. Let him again return to the places. His intelligence, and the habit of observing, will point out to him, whether, from what he has already seen of the country, or from what he will see by multiplying his researches, what are the points whither he ought to betake himself to make his observations, and acquire his data for the solution of the questions which he has proposed to himself. He will not leave the ground until he has solved them, or until he has been convinced of the impossibility of solving them in whole or in part.

It may be considered as superfluous to recommend to the observer to see and note the facts such as they really are, divesting himself of all prejudice, and of all desire to make them enter into a systematic theory. A system is frequently nothing but a coloured-glass, which, placed before the eyes of the naturalist, alters or even changes the colour of the objects seen through it.

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Although we recommend the rejection of all theory not sufficiently founded on facts, and maintain that actual observation is the only true basis of geology, we would notwithstanding recommend to him who devotes himself to its study, not to confine himself to the determination and collection of facts. It is also necessary, as we have already remarked, that he class them, in order to understand their relations, and acquire a general knowledge of their nature. He must combine them, in order to draw inferences from them. It is even necessary that he should endeavour to ascend to a knowledge of their causes; but, in his investigations, he ought always to bear in mind, that all the

conclusions which he draws, all the principles which he endeavours to establish, can be viewed only as consequences of the facts observed, and that all hypothesis is interdicted. If some times the want of a sufficient number of data prevents him arriving at a rigorous solution, and analogy and induction lead him to an inference, he must be careful not to exhibit it with a reality which it does not possess, or to make it one of the foundations of his doctrine. In rearing the edifice of science, the only means he is permitted to employ are observation, the principles of sound physics, and the rules of strict logic.

Observations on the Characters and Affinities of Darwinia, Brunsfelsia, Browallia, Argylia, Eccremocarpus, and of a Plant improperly referred to the latter genus. By Mr DAVID DON, Librarian of the Linnean Society, Member of the Imperial Academy Naturæ Curiosorum, of the Royal Botanical Society of Ratisbon, and of the Wernerian Society of Edinburgh, &c. Communicated by the Author.

DARWINIA.

THIS genus was first proposed by Mr Rudge, in the eleventh

volume of the Transactions of the Linnean Society, where a description and figure of the then only known species, D. fascicularis, is given; but both being probably taken from an imperfect specimen, the structure of the ovarium was left undetermined; which circumstance may sufficiently account for its not having been referred to its proper place in the Natural System. Mr Allan Cunningham, probably misled by the analogous resemblance in habit of Darwinia to Cryptandra, has referred it to the Rhamnec, with which it certainly has no affinity whatever. The examination of a series of specimens, both with flowers and perfect fruit, has convinced me that its true place in the system is among the Myrtaceae, next to Calythrix, with which it agrees in almost every particular, except in the absence of petals. This intimate affinity would not have escaped so experienced an observer as M. Decandolle, had he possessed similar facilities of examination, while engaged in preparing the third volume of his