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whole series of strata which make up its crust. these organic remains-called sometimes fossils,* as being, of all things that are dug out of the earth, those of greatest interest to man in his efforts to penetrate into the past,—that afford most clearly and distinctly the information required concerning the history we need; and it is from them, and from studying the language they speak, that sound conclusions are arrived at in matters of the most interesting detail, as well as in the broadest generalities obtained in our history.

Fossils have sometimes been called the Medals of Creation, and to a certain extent the simile is a just one; for as medals serve to mark either an actual occurrence, or at least the view taken of a supposed occurrence by contemporary authorities, so fossils bear the impress of their date; they mark the condition of the earth at the time and place of their deposit, and in so far therefore at least they are materials for history.

But fossils are much more than mere indications of the history of the time to which they refer. They themselves express the very language of nature; they bear actual, direct, and unquestionable testimony to the course of nature; and when properly considered, and investigated with a view to those analogies which the study of existing nature teaches, they exhibit distinct proof of a long series of successive creations, characterizing different epochs in the earth's progress. They are also found to be, in a very distinct and important sense, characteristic of formations; by which

* From the Latin fossilis,—that which may be dug out of the earth. The word was originally used in English as synonymous with mineral, but has gradually become limited to its present meaning.

it is meant that certain groups of species are chiefly met with in rocks of one age, the various species of each group being more rarely found in those of the preceding and succeeding periods, but never met with again in abundance. And this is not the less true because a few of them, escaping it would seem as if by some unusual powers of endurance, and stragglers from the general herd, have continued to exist for a long time, and through many subsequent periods.

From these two positions, both of which have been satisfactorily proved in the progress of Geology, -namely, that fossils are characteristic of formations, and that in all the different parts of animal and vegetable structure there is reference to every peculiarity of habit in the complete organized being; it follows that the study of fossils becomes an important and necessary branch of Geological research.

There are, however, two ways, by means of each of which satisfactory conclusions have been arrived at from the study of organic remains; and as, of these two, one chiefly bears upon Geology, while the other has reference quite as much to Natural History generally, so both unite in laying the foundation, and building the superstructure, of that general history of the world which it is the true object of Geology to describe.

It is not difficult to explain the value of fossils in each of these two respects. To the Geologist they are of value, not only in the identification of strata in different parts of the same district when the mineral character of the beds is doubtful or variable, but also in determining those groups of strata which shall be either classed together as having something in common, or separated as entirely distinct. Viewed

in this light, they become the groundwork of classification; and every successive observation proves that, when properly and carefully made use of, they are entirely to be depended on, as being not only the best, but the only safe means of separating some strata, and uniting others into groups. Such is their Geological value: and their bearing upon Natural History is no less real or important. They afford numerous links in the great chain of organized beings; they explain difficulties otherwise inexplicable; they suggest reasons and causes for the most extraordinary variations from the ordinary course of nature; and they teach us the important truth, that, throughout all time, there has been a perfectly uniform plan pursued in the construction of the world, and its adaptation for successive races of beings; but that this plan has admitted of innumerable modifications in the manner of carrying it out, all evidently adapted to changing circumstances.

In one word, it is by the proper interpretation of fossils that a science has arisen, unlike any other in its investigations; nobler than any, except Astronomy, in the object at which it aims; and more interesting than any, inasmuch as it combines every branch of Natural History, commonly so called, with those inquiries into a former condition of existence which are best calculated to attract the fancy and excite the imagination. Removed, however, from the condition which it long occupied, as an amusement for speculative men who were contented to imagine for themselves theories of the earth, and propound them for the astonishment, the admiration, or the contempt of the world, Geology has now become the receptacle of innumerable observations, carefully made and

accurately recorded; and from this treasure-house of facts there must soon be derived a theory that will command attention, and a knowledge of laws not less universal than the law of gravitation, or the theory of the solar system. Meantime I propose in the following pages to arrange some of these facts in order, and so present them to notice, that, while the main results which they prove are plainly set before the reader, he need not be deterred from considering them by any too minute reference to the details of the facts themselves, or the circumstances under which they have been discovered or observed.

But I must not proceed to the immediate subject without stating, in a very few words, the nature of the arrangement that I shall follow in my descriptions. In many cases the phenomena themselves, by a due consideration of which groups of strata are distinguished, will be stated and explained; but it will not always be convenient to do this, and in such cases I would have the reader recollect that I have not ventured to draw a line of demarcation unless nature has distinctly indicated it. These lines, however, are not all equally evident. In the whole series of strata exhibited in the British isles, there are, for instance, only two groups so natural, so unquestionable, and so real, that they render the task of classification easy and satisfactory. One of these groups is again subdivided, and this separation also is marked by a great change in organic remains, so that we have three sets of beds, which we may call respectively the Ancient, the Middle, and the Modern, and each of these we may conveniently look upon as denoting a lapse of time which we may call an "Epoch."

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The remaining subdivisions are often very strongly, though not so completely indicated; and to these I shall apply the name " Period," as also sufficiently convenient. It will be found that the different epochs and periods described are in most cases distinguished by a commencement and a termination, often not the less interesting that each exhibits an occasional passage, both by mineral structure and fossil remains, into the beds of the next succeeding one.

In describing the groups of fossils, however, it will be necessary, in order to avoid repetition, that we should as far as possible confine our attention in each case to some group of animals or vegetables whose remains are most characteristic of the particular period which they are assumed to illustrate; and for the sake of convenience we shall often perhaps seem to neglect, or pass by with very slight mention, those which are nevertheless widely distributed in the rocks of the period under consideration. This might lead to some confusion, and even to wrong conclusions, if it were not understood beforehand that such apparent neglect is not without a reason.

In order to remedy this evil in some measure, I have here appended a tabular view of the various periods, in the order in which they will be treated, and with particular reference to the forms of organic life most strikingly exhibited in each. By glancing the eye over this table, the reader, however little acquainted with the details of Geology, will at least be enabled to recognize the plan, and will thus enter on the descriptions with some general notion of their bearing on the whole range of creation.

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