[AD] Jahrb. d. königl. preuss. geologischen Landesanstalt für 1884, p. 438.
[AE] “Die Vergletscherung des Salzachgebietes, etc.”: Geographische Abhandlungen herausgegeben v. A. Penck, Band i. Heft 1.
The limits reached by the inland-ice during its greatest extension are becoming more and more clearly defined, although its southern margin will probably never be so accurately determined as that of the latest epoch of general glaciation. The reasons for this are obvious. When the inland-ice flowed south to the Harz and the hills of Saxony it formed no great terminal moraines. Doubtless many erratics and much rock-rubbish were showered upon the surface of the ice from the higher mountains of Scandinavia, but owing to the fanning-out of the ice on its southward march, such superficial débris was necessarily spread over a constantly-widening area. It may well be doubted, therefore, whether it ever reached the terminal front of the ice-sheet in sufficient bulk to form conspicuous moraines. It seems most probable that the terminal moraines of the great inland-ice would consist of low banks of boulder-clay and aqueous materials-the latter, perhaps, strongly predominating, and containing here and there larger and smaller angular erratics which had travelled on the surface of the ice. However that may be, it is certain that the whole region in question has been considerably modified by subsequent denudation, and to a large extent is now concealed under deposits belonging to later stages of the Pleistocene period. The extreme limits reached by the ice are determined rather by the occasional presence of rock-striæ and roches moutonnées, of boulder-clay and northern erratics, than by recognisable terminal moraines. The southern limits reached by the old inland-ice appear in this way to have been tolerably well ascertained over a considerable portion of central Europe. Some years ago I published a small sketch-map[AF] showing the extent of surface formerly covered by ice. On this map I did not venture to draw the southern margin of the ice-sheet in Belgium further south than Antwerp, where northern erratics were known to occur, but the more recent researches of Belgian geologists show that the ice probably flowed south for some little distance beyond Brussels.[AG] Here and there in other parts of the Continent the southern limits reached by the northern drift have also been more accurately determined, but, so far as I know, none of these later observations involves any serious modification of the sketch-map referred to.
[AF] Prehistoric Europe, 1881.
[AG] See a paper by M. E. Delvaux: Ann. de la. Soc. géol. de Belg., t. xiii. p. 158.
I have now said enough, however, to show that the notion of a general ice-sheet having covered so large a part of Europe, which a few years ago was looked upon as a wild dream, has been amply justified by the labours of those who are so assiduously investigating the peripheral areas of the “great northern drift.” And perhaps I may be allowed to express my own belief that the drifts of middle and southern England, which exhibit the same complexity as the Lower Diluvium of the Continent, will eventually be generally acknowledged to have had a similar origin. I have often thought that whilst politically we are happy in having the sea all round us, geologically we should have gained perhaps by its greater distance. At all events we should have been less ready to invoke its assistance to explain every puzzling appearance presented by our glacial accumulations.
I now pass on to review some of the general results obtained by continental geologists as to the extent of area occupied by inland-ice during the last great extension of glacier-ice in Europe. It is well known that this latest ice-sheet did not overflow nearly so wide a region as that underneath which the lowest boulder-clay was accumulated. This is shown not only by the geographical distribution of the youngest boulder-clay, but by the direction of rock-striæ, the trend of erratics, and the position of well-marked terminal moraines. Gerard de Geer has given a summary[AH] of the general results obtained by himself and his fellow-workers in Sweden and Norway; and these have been supplemented by the labours of Berendt, E. Geinitz, Hauchecorne, Keilhack, Klockmann, Schröder, Wahnschaffe, and others in Germany, and by Sederholm in Finland.[AI] From them we learn that the end-moraines of the ice circle round the southern coasts of Norway, from whence they sweep south-east by east across the province of Gottland in Sweden, passing through the lower ends of Lakes Wener and Wetter, while similar moraines mark out for us the terminal front of the inland-ice in Finland—at least two parallel frontal moraines passing inland from Hango Head on the Gulf of Finland through the southern part of that province to the north of Lake Ladoga. Further north-east than this they have not been traced; but, from some observations by Helmersen, Sederholm thinks it probable that the terminal ice-front extended north-east by the north of Lake Onega to the eastern shores of the White Sea. Between Sweden and Finland lies the basin of the Baltic, which at the period in question was filled with ice, forming a great Baltic glacier which overflowed the Öland Islands, Gottland, and Öland, and which, fanning-out as it passed towards the south-west, invaded, on the south side, the Baltic provinces of Germany, while, on the north, it crossed the southern part of Scania in Sweden and the Danish islands to enter Jutland.
[AH] Zeitschrift d. deutsch. geolog. Ges., Bd. xxxvii., p. 177.
[AI] For papers by Berendt and his associates see especially the Jahrbuch d. k. preuss. geol. Landesanstalt, and the Zaitschr. d. deutsch. geol. Ges. for the past few years. Geinitz: Forsch. z. d. Lands- u. Volkskunde, i. 5; Leopoldina, xxii., p. 37; I. Beitrag z. Geologie Mecklenburgs, 1880, pp. 46, 56. Sederholm: Fennia, I. No. 7.