NATURAL AND ARTIFICIAL CHARACTERS.

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ber and situation of the stamens, and pistils, and hence such characters are artificial or arbitrary. But those plants which are alike in anatomical structure, correspond in most of their properties; and such characters, therefore, are natural.

Inf. 1. In applying this principle to rocks, we find first, that their division into stratified and unstratified is natural: that is, it brings together those kinds whose origin and other important characters are similar. Now we shall find that this division enters into nearly all the more recent systems of classification that have been described.

Inf. 2. In the division of the rocks into fossiliferous and nonfossiliferous, all geologists agree: And in fact there is scarcely a possibility of disagreement on this point. So that here we have another important natural character as the basis of classification.

Inf. 3. In nearly all the systems of classification, the larger formations coincide; which is a presumptive proof that they are natural; since so many different observers agree in forming their boundaries. These formations ought perhaps to be regarded as the Species in Geology.

Inf. 4. Classification founded upon the relative age of different rocks, is entirely natural, because all observers agree that they were produced at different times. But as superposition and organic remains are the only safe criteria of relative age, there is ground for a diversity of opinion in assigning places to the different formations; since these criteria can be ascertained sometimes only imperfectly.

Inf. 5. Characters dependent upon theoretical considerations are artificial, since few of the theories are so certainly settled as not to be liable to considerable modification. Hence such terms as Primary, Transition, Secondary, Tertiary, Diluvial, &c. are objectionable, if they are not understood to refer simply to superposition.

How

Rem. Neology is often a greater evil in science than the continued use of objectionable terms; continued, I mean, until terms are proposed which are so decidedly good as to force themselves into use. It is partly on this ground that the terms, Primary, Transition, Secondary, Tertiary, and Diluvial, still continue in use. But it is partly, also, because, apart from theoretical views, there does exist in nature some foundation for a division of the rocks into groups of this sort. well marked, for instance, is the distinction between the tertiary and the secondary group; and how difficult will it be to strike out from American geology such a deposit as diluvium. I know not why the ingenious arrangement of Mr. Conybeare has not been adopted, unless it be because it simply indicates superposition; and geologists feel as if this did not express the whole truth in respect to the larger groups of rocks; and therefore prefer to use terms which mean too much, rather than such as fall short of the truth.

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ELEMENTS OF THE ROCKS.

Inf. 6. Characters founded upon lithological distinctions are artificial, for the same reason that those derived from the number of stamens and pistils are bad in botany.

Inf. 7. Discrepancy in classification often springs from carrying the subdivisions of a formation too far, for the same reason that characters in botany and zoology could not be`depended on, that were derived from the varieties of a species.

Inf. 8. Finally, it appears that in all the essential principles of the classification of rocks, geologists are nearly agreed. They all admit one class to be stratified and another unstratified:-one portion of the stratified rocks to be fossiliferous and another portion not fossiliferous. And they generally agree, also, as to the extent of the different distinct formations; although some would make their number greater than others,--just as it is in respect to species in mineralogy, botany, and zoology. Now these three principles are all that are essential for classification; and some of the best geologists, as may be seen by the Table, limit themselves to these. But if others choose to subdivide the formations still farther, and to refer the groups to primary, secondary, &c. classes, even though they differ widely here, it must not be hence inferred that they are at variance in respect to the essential principles of classification.

SECTION II.

THE CHEMISTRY AND MINERALOGY OF GEOLOGY.

Descr. Of the fifty-four simple substances hitherto discovered, sixteen constitute by their various combinations, nearly the whole of the matter yet known to enter into the composition of the globe. They are as follows, arranged in three classes, according to their amount; the first in each class being most abundant.

1. Metalloids, or the bases of the earths and alkalies.

1. Silicium. 2. Aluminium. 3. Potassium. 4. Sodium. 5. Magnesium. 6. Calcium.

2. Metals Proper.

1. Iron. 2. Manganese.

3. Non Metallic Substances.

SIMPLE MINERALS IN THE ROCKS.

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1. Oxygen. 2. Hydrogen. 3. Nitrogen. 4 Carbon. 5. Sulphur. 6. Chlorine. 7. Fluorine. 8. Phosphorus. De la Beche's Researches in Theoretical Geology, p 22. Amherst, 1837.

Descr. The metallic substances mentioned above, united with oxygen, constitute the great mass of the rocks, consolidated and unconsolidated, accessible to man. Oxygen also forms twenty per cent of the atmosphere, and one third part by measure of water. Hydrogen forms the other two thirds of this latter substance; and it is evolved also from volcanos, and is known. to exist in coal. Nitrogen forms four fifths of the atmosphere, and enters into the composition of animals, living and fossil. It is found also in coal. Carbon, however, forms the principal part of coal; and it exists likewise in the form of carbonic acid in the atmosphere, though constituting only one thousandth part. (Liebig's Organic Chemistry, p. 74. Amer. Edition, 1841.) and it forms an important part of all the carbonates, and is produced wherever vegetable and animal matters are undergoing decomposition. Sulphur is found chiefly in the sulphurets and sulphates that are so widely disseminated. Chlorine is found

chiefly in the ocean, and in the rock salt dug out of the earth. Fluorine occurs in most of the rocks, though in small proportion. Still less is the amount of phosphorus, though widely diffused in the rocks and soils, and abundant in organic remains.

Descr. Nearly all the simple substances above mentioned ave entered into their present combinations as binary comounds; that is, they were united two and two before forming the present compounds in which they are found. The following constitute nearly all the binary compounds of the accessible parts of the globe.

1. Silica 2. Alumina. 3 Lime. 4. Magnesia. 5. Potassa. 6. Soda. 7. Oxide of Iron. 8. Oxide of Manganese. 9. Water 10. Carbonic Acid.

Obs. It is meant only that these binary compounds, and the sixteen simple substances that have been enumerated, constitute the largest part of the known mass of the globe: for many other binary compounds, and probably all the known simple substances are found in small quantity in the rocks; but not enough to be of importance in a geological point of view.

Descr. It has been calculated that oxygen constitutes 50 per cent. of the ponderable matter of the globe, and that its crust contains 45 per cent. of silica, and at least 10 per cent. of alumina. Potassa constitutes nearly 7 per cent. of the unstratified rocks, and enters largely into the composition of some of the stratified class. Soda forms nearly 6 per cent of some basalts and other less extensive unstratified rocks; and it enters largely into the composition of the ocean. Lime and magnesia are