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SUBJECTS TREATED OF IN THIS WORK.
barrier to all attempts to trace farther back into the past the signs of the existence of Man upon the earth.
In the concluding chapters I shall offer a few remarks on the recent modifications of the Lamarckian theory of progressive development and transmutation, which are suggested by Mr. Darwin's work on the Origin of Species, by Variation and Natural Selection,' and the bearing of this hypothesis on the different races of mankind and their connection with other parts of the animal kingdom.
Nomenclature.- Some preliminary explanation of the nomenclature adopted in the following pages will be indispensable, that the meaning attached to the terms Recent, Post-pliocene, and Post-tertiary may be correctly understood.
Previously to the year 1833, when I published the third volume of the · Principles of Geology,' the strata called Tertiary had been divided by geologists into Lower, Middle, and Upper; the Lower comprising the oldest formations of the environs of Paris and London, with others of like age; the Middle, those of Bordeaux and Touraine; and the Upper, all that lay above or were newer than the last-mentioned group.
When engaged, in 1828, in preparing for the press the treatise on geology above alluded to, I conceived the idea of classing the whole of this series of strata according to the different degrees of affinity which their fossil testacea bore to the living fauna. Having obtained information on this subject during my travels on the Continent, I learnt that M. Deshayes of Paris, already celebrated as a conchologist, had been led independently, by the study of a large collection of recent and fossil shells, to very similar views respecting the possibility of arranging the tertiary formations in chronological order, according to the proportional number of species of shells identical with living ones, which characterised each of the successive groups above mentioned. After comparing 3000 fossil species with 5000 living ones, the result arrived at was, that in the lower tertiary strata, there were about 31 per cent. identical with recent; in the middle tertiary (the faluns of the Loire and Gironde), about 17 per cent. ; and in the upper tertiary, from 35 to 50, and sometimes in the most modern beds as much as 90 to 95 per cent. For the sake of clearness and brevity, I proposed to give short technical names to these sets of strata, or the periods to which they respectively belonged. I called the first or oldest of them Eocene, the second Miocene, and the third Pliocene. The first of the above terms, Eocene, is derived from nós eos, dawn, and xausvos kainos, recent; because an extremely small proportion of the fossil shells of this period could be referred to living species, so that this era seemed to indicate the dawn of the present testaceous fauna, no living species of shells having been detected in the antecedent or secondary rocks.
Some conchologists are now unwilling to allow that any Eocene species of shell has really survived to our times so unaltered as to allow of its specific identification with a living species. I cannot enter in this place into this wide controversy. It is enough at present to remark, that the character of the Eocene fauna, as contrasted with that of the antecedent secondary formations, wears a very modern aspect, and that some able living conchologists still maintain that there are Eocene shells not specifically distinguishable from those now extant; though they may be fewer in number than was supposed in 1833.
The term Miocene (from usiwe meion, less; and xasós kainos, recent) is intended to express a minor proportion of recent species (of testacea); the term Pliocene (from a reiw pleión, more; and raivos kainos, recent), a comparative plurality of the same.
It has sometimes been objected to this nomenclature that certain species of infusoria found in the chalk are still existing, and, on the other hand, the Miocene and Older CHAP. I.
RECENT, POST-PLIOCENE, AND POST-TERTIARY.
Pliocene deposits often contain the remains of mammalia, reptiles, and fish, exclusively of extinct species. But the reader must bear in mind that the terms Eocene, Miocene, and Pliocene were originally invented with reference purely to conchological data, and in that sense have always been and are still used by me.
Since the first introduction of the terms above defined, the number of new living species of shells obtained from different parts of the globe has been exceedingly great, supplying fresh data for comparison, and enabling the paleontologist to correct many erroneous identifications of fossil and recent forms. New species also have been collected in abundance from tertiary formations of every age, while newly discovered groups of strata have filled up gaps in the previously known series. Hence modifications and reforms have been called for in the classification first proposed. The Eocene, Miocene, and Pliocene periods have been made to comprehend certain sets of strata of which the fossils do not always conform strictly in the proportion of recent to extinct species with the definitions first given by me, or which are implied in the etymology of those terms. These innovations have been treated of in my Elements or Manual of Elementary Geology, and in the Supplement to the fifth edition of the same, published in 1859, where some modifications of my classification, as first proposed, are introduced ; but I need not dwell on these on the present occasion, as the only formations with which we shall be concerned in the present volume are those of the most modern date, or the Post-tertiary. It will be convenient to divide these into two groups, the Recent and the Post-pliocene. In the Recent we may comprehend those deposits in which not only all the shells but all the fossil mammalia are of living species; in the Post-pliocene those strata in which, the shells being recent, a portion, and often a considerable one, of the accompanying
fossil quadrupeds belongs to extinct species. I am aware that it may be objected, with some justice, to this nomenclature, that the term Post-pliocene ought in strictness to include all geological monuments posterior in date to the Pliocene; but when I have occasion to speak of these in the aggregate, I shall call them Post-tertiary, and reserve the term Postpliocene exclusively for Lower Post-pliocene, the Upper Postpliocene formations being called · Recent.'
Cases will occur where it may be scarcely possible to draw the line of demarcation between the Newer Pliocene and Postpliocene, or between the latter and the recent deposits; and we must expect these difficulties to increase rather than diminish with every advance in our knowledge, and in proportion as gaps are filled up in the series of geological records.
In 1839 I proposed the term Pleistocene as an abbreviation for Newer Pliocene, and it soon became popular, because adopted by the late Edward Forbes in his admirable essay on “The Geological Relations of the existing Fauna and Flora of the British Isles ;'* but he applied the term almost precisely in the sense in which I shall use Post-pliocene in this volume, and not as short for Newer Pliocene. In order to prevent confusion, I think it best entirely to abstain from the use of Pleistocene in future; I have found that the introduction of such a fourth name (unless restricted solely to the older Post-tertiary formations) must render the use of Pliocene, in its original extended sense, impossible, and it is often almost indispensable to have a single term to comprehend both divisions of the Pliocene period.
The annexed tabular view of the whole series of fossiliferous strata will enable the reader to see at a glance the chronological relation of the Recent and Post-pliocene to the antecedent periods.
* Geological Relations of the Survey of Great Britain, vol. i. p. 336. existing Fauna and Flora of the London, 1846.) British Isles. (Memoirs of Geological
10. MAESTRICHT BEDS.
RIASSIC. MUSCHELKALK. 27. LOWER TRIAS. 28. PERMIAN, MAGNESIAN LIMESTONE.)
| PERMIAN. 29. COAL-MEASURES. 30. CARBONIFEROUS CARBONIFEROUS.
LIMESTONE. 31. UPPER)
\ DEVONIAN. DEVONIAN, 32. LOWERS 33. UPPER
SILURIAN. SILURIAN. 34. LOWER) 38. UPPER
SCAMBRIAN. 36. LOWERS