But in our reasonings and examples we shall mainly confine ourselves to the physical sciences; and for the most part to Geology, which in the History I have put forwards as the best representative of the Palætiological Sciences.
CHAPTER II.
Of the Three Members of a Palætiological Science.
1. Divisions of such Sciences.—In each of the Sciences of this class we consider some particular order of phenomena now existing:—from our knowledge of the causes of change among such phenomena, we endeavour to infer the causes which have made this order of things what it is:—we ascend in this manner to some previous stage of such phenomena;—and from that, by a similar course of inference, to a still earlier stage, and to its causes. Hence it will be seen that each such science will consist of two parts,—the knowledge of the Phenomena, and the knowledge of their Causes. And such a division is, in fact, generally recognized in such sciences: thus we have History, and the Philosophy of History; we have Comparison of Languages, and the Theories of the Origin and Progress of Language; we have Descriptive Geology, and Theoretical or Physical Geology. In all these cases, the relation between the two parts in these several provinces of knowledge is nearly the same; and it may, on some occasions at least, be useful to express the distinction in a uniform or general manner. The investigation of Causes has been termed Ætiology by philosophical writers, and this term we may use, in contradistinction to the mere Phenomenology of each such department of knowledge. And thus we should have Phenomenal Geology and Ætiological Geology, for the two divisions of the science which we have above termed Descriptive and Theoretical Geology.
2. The Study of Causes.—But our knowledge respecting the causes which actually have produced any [264] order of phenomena must be arrived at by ascertaining what the causes of change in such matters can do. In order to learn, for example, what share earthquakes, and volcanoes, and the beating of the ocean against its shores, ought to have in our Theory of Geology, we must make out what effects these agents of change are able to produce. And this must be done, not hastily, or unsystematically, but in a careful and connected manner; in short, this study of the causes of change in each order of phenomena must become a distinct body of Science, which must include a large amount of knowledge, both comprehensive and precise, before it can be applied to the construction of a theory. We must have an Ætiology corresponding to each order of phenomena.
3. Ætiology.—In the History of Geology, I have spoken of the necessity for such an Ætiology with regard to geological phenomena: this necessity I have compared with that which, at the time of Kepler, required the formation of a separate science of Dynamics (the doctrine of the Causes of Motion), before Physical Astronomy could grow out of Phenomenal Astronomy. In pursuance of this analogy, I have there given the name of Geological Dynamics to the science which treats of the causes of geological change in general. But, as I have there intimated, in a large portion of the subject the changes are so utterly different in their nature from any modification of motion, that the term Dynamics, so applied, sounds harsh and strange. For in this science we have to treat, not only of the subterraneous forces by which parts of the earth’s crust are shaken, elevated, or ruptured, but also of the causes which may change the climate of a portion of the earth’s surface, making a country hotter or colder than in former ages; again, we have to treat of the causes which modify the forms and habits of animals and vegetables, and of the extent to which the effects of such causes can proceed; whether, for instance, they can extinguish old species and produce new. These and other similar investigations would not be naturally included in the notion of Dynamics; and therefore it [265] might perhaps be better to use the term Ætiology when we wish to group together all those researches which have it for their object to determine the laws of such changes. In the same manner the Comparison and History of Languages, if it is to lead to any stable and exact knowledge, must have appended to it an Ætiology, which aims at determining the nature and the amount of the causes which really do produce changes in language; as colonization, conquest, the mixture of races, civilization, literature, and the like. And the same rule applies to all sciences of this class. We shall now make a few remarks on the characteristics of such branches of science as those to which we are led by the above considerations.
4. Phenomenology requires Classification. Phenomenal Geology.—The Phenomenal portions of each science imply Classification, for no description of a large and varied mass of phenomena can be useful or intelligible without classification. A representation of phenomena, in order to answer the purposes of science, must be systematic. Accordingly, in giving the History of Descriptive or Phenomenal Geology, I have called it Systematic Geology, just as Classificatory Botany is termed Systematic Botany. Moreover, as we have already seen, Classification can never be an arbitrary process, but always implies some natural connexion among the objects of the same Class; for if this connexion did not exist, the Classes could not be made the subjects of any true assertion. Yet though the classes of phenomena which our system acknowledges must be such as already exist in nature, the discovery of these classes is, for the most part, very far from obvious or easy. To detect the true principles of Natural Classes, and to select marks by which these may be recognized, are steps which require genius and good fortune, and which fall to the lot only of the most eminent persons in each science. In the History, I have pointed out Werner, William Smith, and Cuvier, as the three great authors of Systematic Geology of Europe. The mode of classifying the materials of the earth’s surface which was found, by these philosophers, fitted to [266] enunciate such general facts as came under their notice, was to consider the rocks and other materials as divided into successive layers or strata, superimposed one on another, and variously inclined and broken. The German geologist distinguished his strata for the most part by their mineralogical character; the other two, by the remains of animals and plants which the rocks contained. After a beginning had thus been made in giving a genuine scientific form to phenomenal geology, other steps followed in rapid succession, as has already been related in the History[5]. The Classification of the Strata was fixed by a suitable Nomenclature. Attempts were made to apply to other countries the order of strata which had been found to prevail in that first studied: and in this manner it was ascertained what rocks in distant regions are the synonyms, or Equivalents[6],—of each other. The knowledge thus collected and systematized was exhibited in the form of Geological Maps.
[5] Hist. Ind. Sc. b. xviii. c. iii.
[6] Ib. sect. 4.