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Published online by Cambridge University Press: 06 July 2012
For many years geologists have recognised the occurrence of at least two boulder-clays in the British Islands and the corresponding latitudes of the Continent. It is no longer doubted that these are the products of two separate and distinct glacial epochs. This has been demonstrated by the appearance of intercalated deposits of terrestrial, freshwater, or, as the case may be, marine origin. Such interglacial accumulations have been met with again and again in Britain, and they have likewise been detected at many places on the Continent, between the border of the North Sea and the heart of Russia. Their organic contents indicate in some cases cold climatic conditions; in others, they imply a climate not less temperate or even more genial than that which now obtains in the regions where they occur. Nor are such interglacial beds confined to northern and north-western Europe. In the Alpine Lands of the central and southern regions of our Continent they are equally well developed. Impressed by the growing strength of the evidence, it is no wonder that geologists, after a season of doubt, should at last agree in the conclusion that the glacial conditions of the Pleistocene period were interrupted by at least one protracted interglacial epoch. Not a few observers go further, and maintain that the evidence indicates more than this. They hold that three or even more glacial epochs supervened in Pleistocene times. This is the conclusion I reached many years ago, and I now purpose reviewing the evidence which has accumulated since then, in order to show how far it goes to support that conclusion.
page 130 note * Neues Jahrbuch f. Min. Geol. u. Palæont., 1891, ii. pp. 62, 228; Ibid., 1892, i. p. 114.
page 131 note * Naturwissenschaftliche Wochenschrift, Bd. vii. (1892), No. 4, p. 31Google Scholar. The plants were determined by Dr Weber, Professor Wittmack, and Herr Warnstorf. [More recent investigations have considerably increased our knowledge of this flora. See Naturwissenschaftliche Wochenschrift, Bd. vii. (1892), Nr. 24, 25Google Scholar. Ausland, 1892, Nr. 20.]
page 132 note * Beskrifning. till geol. Kartbl. Trolleholm: Sveriges Geologiska Undersökning, Ser. Aa. Nr. 87.
page 132 note † Om de äldre baltiska isströmmen i södra Sverige: Geolog. Förening. a Stockholm Förhandl., Bd. x. p. 157.
page 133 note * Bull, de la Soc. Imper. des Naturalistes de Moskau, No. 4, 1890.
page 135 note * Geol. Mag., 1881, p. 354.
page 137 note * Morlot, , Bulletin de la Soc. Vaud. d. Sciences nat., 1854, 1858, 1860Google Scholar; Deicke, , Bericht. d. St. Gall, naturf. ges., 1858Google Scholar; Heer, , Urwelt der SchweizGoogle Scholar; Muhlberg, , Festschrift d. aarg. naturf. Ges. z. Feier ihrer 500 Sitz., 1869Google Scholar; Rothpletz, , Denkschr. d. schweizer. Ges. f. d. ges. Naturwissensch., Bd. xxviii., 1881Google Scholar; Wettstein, , Geologie v. Zurich u. Umgebung, 1885Google Scholar; Baltzer, , Mitteil. d. naturf. Ges Bern, 1837Google Scholar; Renevier, , Bull, de la Soc. helvèt. d. Sciences nat., 1887.Google Scholar
page 137 note † Penck, , Die Vergletscherung d. deutschen Alpen, 1882Google Scholar; Brückner, , “Die Vergletsclierung des Salzachgebietes,” Geogr. Ahhandl. Wien, Bd. i.Google Scholar; Böhm, , Jahrb. der k. k. geol. Reichsanst, 1884, 1885Google Scholar; see also Fraas, O., Neues Jahrb. f. Min. Geol. u. Palæont, 1880, Bd. i. p. 218Google Scholar; Fugger, E. and Kastner, C., Verhandl. d. k. k. geol. Reichsanst, 1883, p. 136Google Scholar.
page 138 note * Mittheil. des deutsch. u. oesterreich. Alpenvereins, 1890, No. 20 u. 23.
page 138 note † Beiträge z. geolg. Karte der Schweiz, 31 Lief., 1891; Archiv. d. Sciences phys. et nat., 1891, p. 44.
page 138 note ‡ “Die grosse Eiszeit,” Himmel u. Erde.
page 138 note § Penck, Die Vergletscherung der deutschen Alpen, p. 228; Verhandl. d. k. k. geol. Reichsanst., 1887, No. 5; Himmel und Erde, 1891. Böhm, Jahrb. d. k. k. geol. Reichsanst, 1884, p. 147. Blaas, , Ferdinandeums Zeitschr., iv.Google Scholar Folge; Bericht. d. nat.-wissensch. Vereins, 1889, p. 97.
page 138 note § Des phénomènes glaciaires dans le Plateau central de la France, &c, Paris, 1869Google Scholar.
page 139 note * Bull. Soc. géol. de France, 1884; see also Boule, M., Bull, de la Soc. philomath, de Paris, 8e Sér. i. p. 87Google Scholar.
page 139 note † Garrigou, , Bull. Soc. géol de France, 2e Sér. xxiv. p. 577Google Scholar; Jeanbernat, , Bull, de la Soc. d'Hist. nat. de Toulouse, iv. pp. 114, 138Google Scholar; Piette, , Bull. Soc. géol. de France, 3e Sér. ii. pp. 503, 507Google Scholar.
page 139 note ‡ Mitteilungen d. Vereins f. Erdkunde zu Leipzig, 1883.
page 140 note * For a particular account of the Tay-valley Succession, see Prehistoric Europe, p. 385.
page 140 note † Proc. Roy. Soc. Edin., 1883–84, p. 745; Mem. Geol. Survey, Scotland, Explanation of Sheet 31.
page 140 note * Prehistoric Europe, chaps, xvi., xvii.
page 141 note * British Association Reports (1854): Trans. of Sections, p. 78.
page 141 note † L. Hinxman: Paper read before Edin. Geol. Soc., April 1892.
page 141 note ‡ Prehistoric Europe (chaps, xvi. xvii.) gives a fuller statement of the evidence.
page 142 note * Sitzungsberichte d. Kais. Acad. d. Wissensch. in Wien, mathem,-naturw. Classe, Bd. xcvii. Abth. i., 1888Google Scholar.
page 143 note * In some places, however, certain marine deposits (Leda-myalis bed) immediately overlie the Forest-bed. See postea, footnote, p. 145.
page 144 note * Mem. of Geol. Survey, “Pliocene Deposits of Britain.”
page 145 note * The inference that the Forest-bed occupies an interglacial position is strengthened by the evidence of certain marine deposits which immediately overlie it. These (known collectively as the Leda-myalis bed) occur in irregular patches, which, from the character of their organic remains, cannot all be precisely of the same age. In one place, for example, they are abundantly charged with oysters, having valves united, and with these are associated other species of molluscs that still live in British Seas. At another place no oysters occur, but the beds yield two Arctic shells, Leda myalis and Astarte borealis, and some other forms which have no special significance. Professor Otto Torell pointed out to Mr Reid that these separate deposits could not be of the same age, for the oyster is sensitive to cold and does, not inhabit the seas where Leda myalis and Astarte borealis flourish. From a consideration of this and other evidence Mr Reid concludes that it is possible that the deposits indicate a period of considerable length, during which the depth of water varied and the climate changed. Two additional facts may be noted: Leda myalis does not occur in any of the underlying Pliocene beds, while the oyster is not found in the Weybourn and Chillesford Crag, though common lower down in the Pliocene series. These facts seem to me to have a strong bearing on the climatic conditions of the Forest-bed epoch. They show us that the oyster flourished in the North Sea before the period of the Weybourn Crag—that it did not live side by side with the Arctic forms of that period—and that it reappeared in our seas when favourable conditions returned. When the climate again became cold an Arctic fauna (including a new-comer, Leda myalis) once more occupied the North Sea.
page 145 note † Elephas meridionalis is usually regarded as a type-form of the Newer Pliocene, but long ago Dr Fuchs pointed out that in Hungary this species is of quaternary age: Verhandl. d. k. h. geolog. Reichsanstalt, 1879, pp. 49, 270. It matters little whether we relegate to the top of the Pliocene or to the base of the Pleistocene the beds in which this species occurs. That it is met with upon an interglacial horizon is certain; and if we are to make the Pleistocene co-extensive with the glacial and interglacial series, we shall be compelled to include in that system some portion of the Newer Pliocene.
page 145 note ‡ Julien, Des Phénomènes glaciavres dans le Plateau central, &c, 1869; Boule, Revue d'Anthropologie, 1879.
page 145 note § Prehistoric Europe, p. 306. Professor Penck writes me that he and the Swiss glacialist, Dr Du Pasquier, have recently examined these deposits, and are able to confirm my conclusion as to their interglacial position.
