[CJ] Penck: _Die Vergletscherung d. deutschen Alpen_, 1882. Brückner: "Die Vergletscherung des Salzachgebietes," _Geogr. Abhandl. Wien_, Bd. i. Böhm: _Jahrb. der k. k. geol. Reichsanst._, 1884, 1885. See also O. Fraas, _Neues Jahrb. f. Min. Geol. u. Palæont._, 1880, Bd. i. p. 218; E. Fugger and C. Kastner, _Verhandl. d. k. k. geol. Reichsanst._, 1883, p. 136. [CK] _Mittheil. des deutsch. u. oesterreich. Alpenvereins_, 1890, No. 20 u. 23. [CL] _Beiträge z. geolog. Karte der Schweiz_, 31 Lief., 1891; _Archiv. d. Sciences phys. et nat._, 1891, p. 44. [CM] "Die grosse Eiszeit," _Himmel u. Erde_. Although the occurrence of such sub-äerial products intercalated between separate morainic accumulations is evidence of climatic changes, still it does not tell us how far the glaciers retreated during an interglacial stage. Fortunately, however, lignite beds and other deposits charged with plant remains are met with occupying a similar position, and from these we gather that during interglacial times the glaciers sometimes retired to the very heads of the mountain-valleys, and must have been smaller than their present representatives. Of such interglacial plant-beds, which have been met with in some twenty localities, the most interesting, perhaps, is the breccia of Hötting, in the neighbourhood of Innsbruck.[CN] This breccia rests upon old morainic accumulations, and is again overlaid by the later moraines of the great Inn glacier. From the fact that the breccia yielded a number of supposed extinct species of plants, palæontologists were inclined to assign it to the Pliocene. Professor Penck, however, prefers to include it in the Pleistocene system, along with all the glacial and interglacial deposits of the Alpine Lands. According to Dr. von Wettstein, the flora in question is not Alpine but Pontic. At the time of the formation of the breccia the large-leaved _Rhododendron ponticum_ flourished in the Inn Valley at a height of 1200 metres above the sea; the whole character of the flora, in short, indicates a warmer climate than is now experienced in the neighbourhood of Innsbruck. It is obvious, therefore, that in interglacial times the glaciers must have shrunk back, as Professor Penck remarks, to the highest ridges of the mountains. [CN] 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. Folge; _Bericht. d. naturwissensch. Vereins_, 1889, p. 97.