Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments / by Sir Charles Lyell.

  • Lyell, Charles, Sir, 1797-1875.
Date:
1865
Catalogue details

Licence: Public Domain Mark

Credit: Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments / by Sir Charles Lyell. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    238/822 (page 216)
    LINE BETWEEN MIOCENE AND EOCENE. [Ch. XIV. his classical work on the fossil shells of the environs of Paris (1824— 37) he had described twenty-nine species from the Fontainebleau sands, of which some few could be identified with fossils belonging to the older Calcaire Grossier, whereas no one of them was common to the faluns of Touraine. He also insisted on the general aspect or facies of the fauna bearing a far greater resemblance to the testacea of the older or Eocene group than to that of the faluns. A few years after the publication of my “ Principles of Geology ” (vol. iii.) in 3 833, the directors of the Government Survey of France, MM. Dufrenoy and E. de Beaumont, referred the Paris gypsum in then- geological map to the Eocene, and the overlying marine sands and Calcaire de la Beauce to the Miocene, the faluns of Touraine being re- garded by them as constituting an upper division of the same Miocene series. M. d’Archiac, in 1839, adopted the same method; and M. Alcide d’Orbigny, in his Paleontology in 1852, classed the Gres de Fontaine- bleau, or “ Sables Superieurs,” as “Falunien A,” and the faluns of the Loire as “Falunien B,” thus giving in his adhesion to the same system of classification. That there should have been much differ- ence of opinion on this subject was very natural, for, at the time when I first took part in the controversy, there seemed very little prospect of bridging over the wide gap between the two formations which it was thus proposed to link together in one group. In 1857, by aid of a railway cutting at Etampes, the number of marine shells derived from the Fontainebleau sands was suddenly raised from 29 to 90 species. The newly-discovered fossils furnished arguments both for and against the views of those who desired to refer the strata containing them to the Miocene rather than to the Eocene series. As bearing against those views, may be mentioned the fact that none of the 90 shells agreed with species proper to the faluns of the Loire, while some of them were identical with Calcaire Grossier species. This was the more worthy of note because Etampes is within seventy miles of Pontlevoy, near Blois, and not more than 100 miles from Savigne, near Tours, two localities where the falunian shells are very abundant. So striking a difference between the species of the valley of the Loire and those of the basin of the Seine, when we consider the contiguity of the spots above alluded to, could not be the result of geographical distribution at one and the same era, but must evidently have depended on a great difference in the age of the de- posits. It marked the influence of Time, and not of Space. On the other hand, in favour of grouping the Etampes or Fon- tainebleau sands with the newer Falunian rather than with the older Eocene formations, M. Hebert pointed out that a majority of the 90 Etampes and Gres de Fontainebleau fossils agreed specifically with shells which, in Belgium, Mayence, and other localities, had been shown by the labours of MM. Dumont, Nyst, De Ivoninck, and Bosquet to occupy a very distinct geological position above the typical Eocene series of the Paris basin, and of which the equiva- lents at Mayence hrtd long been recognized as Miocene. M. Hebert also published, in 1855, a map descriptive of the areas of two tertiary