488 



NA TURE 



[Sept. 19, 1889 



as that of the latest epoch of general glaciatlon. 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 

 nioraines. 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 debris 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 con- 

 taining 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 con- 

 siderably modified by subsequent denudation, and to a large 

 extent is now concealed under deposits beloniiing to later stages 

 of the Pleistocene period. The extreme limits reached by the 

 ice are determined rather by the occasional presence of rock- 

 strice and roclies inoutonnks, of bouWer-clay and northern 

 erratics, than by recognizable 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 (" Prehistoric Europe," 1881) 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 (see a paper by M. E. Delvaux, Ann. de la 

 Soc. geol. de Btlg., t. xiii. p. 158). 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. 



I have now said enough, however, toshow 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 investi- 

 gating 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 geo- 

 graphical distribution of the youngest boulder-clay, but by the 

 direction of rockstrise, the trend of erratics, and the position of 

 well-marked moraines. Gerard de Geer has given a sum- 

 mary (Zeitschrift d. deutsch. geolog. Ges., Bd. xxxvii. p. 177) 

 of the general results obtained liy himself and his fellow-workers 

 in Sweden and Norway ; and these have been supplemented by 

 the labours of Berendt, Geinitz, Hunchecorne, Keilhack, Klock- 

 mann, Schroder, Wahnschaffe, and others in Germany, and by 

 Sede'rholm in Finland. ^ 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, Sederbolm 



' For papers by Berendt and hi.s associates see especially the Jahrbiick 

 d. k. prcnss. geol. Landesanstalt, and the Zeitschr. d. deutsch. geol. Ges. 

 for the past few years. Geinitz, Forsch. z. d. Landes- it. Volkskundc, i. 5 ; 

 Leepoldina, x.ai. p. 37 ; /. Beltrag z. Geologie Mecklenbu'gs, 1880, pp. 46, 

 56. Sederholm, Fennia, i. No. 7. 



thinks it probable that, the terniinal 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, form- 

 ing a oreat Baltic glacier, which overflowed the Aland Islands, 

 Gottland, and Oland, and which, fanning-out as it passed to- 

 wards the south-west, invaded, on the south side, the Baltic 

 provinces of Germany, while, on the north, it cros-^ed the 

 southern part of Scania in Sweden and the Danish islands to 

 enter upon Jutland. 



The upper boulder-clay of those regions is now recognized as 

 the ground-moraine of this latest ice-sheet. In many places it is 

 separated from the older boulder-clay by interglacial deposits, 

 some of which are marine, while others are of fresh-water and 

 terrestrial origin. During interglacial times the sea that over- 

 flowed a considerable portion of North Germany was evidently 

 continuous with the North Sea, as is shown not only by the 

 geographical distribution of the interglacial marine deposits, but 

 by their North Sea fauna. German geologists generally group all 

 the interglacial deposits together, as if they belonged to one and 

 the same interglacial epoch. This perhaps we must look upon 

 as only a provisional arrangement. Certain it is that the fresh- 

 water and terrestrial beds which frequently occur on the same or 

 a lower level, and at no great distance from the marine deposits, 

 cannot in all cases be contemporaneous with the latter. Pos- 

 sibly, however, such discordances may be accounted for by 

 oscillations in the level of the interglacial sea — land and water 

 having alternately prevailed over the same area. Two boulder- 

 clays, as we have seen, have been recognized over a wide region 

 in North Germany. In some places, however, three or more 

 such boulder-clays have been observed overlying one another 

 throughout considerable areas, and these clays are described as 

 being distinctly separate and distinguishable the one from the 

 other. ^ Whether they with their intercalated aqueous deposits 

 indicate great oscillations of one and the same ice-sheet — now 

 advancing, now retreating — or whether the stony clays may not 

 be the ground- moraines of fo many different ice-sheets, separated 

 the one from the other by true interglacial conditions, future 

 investigations must be left to decide. 



The general conclusions arrived at by those who are at pre- 

 sent investigating the glacial accumulations of Northern Europe 

 may be summarized as follows : — 



1. Before the invasion of Northern Germany by the inland ice 

 the low grounds bordering on the Baltic were overflowed by a 

 sea which contained a boreal and arctic fauna. These marine 

 conditions are indicated by the presence under the lower boulder- 

 clay of more or less well-bedded fossiliferous deposits. On the 

 same horizon occur also beds of sand, containing fresh-water 

 shells, and now and again mammalian remains, some of which 

 imply cold and others temperate climatic conditions. Obviously 

 all these deposits may pertain to one and the same period, or 

 more properly to different stages of the same period — some 

 dating back to a time when the climate was still temperate, 

 while others clearly indicate the prevalence of cold conditions, 

 and are therefore probably somewhat younger. 



2. The next geological horizon in ascending order is that 

 which is marked by the "lower diluvium "—the glacial and 

 fluvio-glacial detritus of the great ice-sheet which flowed south 

 to the foot of the Harz Mountains, The boulder clay on this 

 horizon now and again contains marine, fresh- water, and ter- 

 restrial organic remains, derived undoubtedly from the so-called 

 preojlacial beds already referred to. These latter, it would ap- 

 pear, were ploughed up and largely incorporated with the old 

 ground-moraine. 



3. The interglacial beds which next succeed contain remains 

 of a well-marked temperate fauna and flora, which point to 

 something more than a mere partial or local retreat of the inland 

 ice. The geographical distribution of the beds and the presence 

 in these of such forms as Elephas antiqtcns, Cervits elephas, C. 

 inegaceros, and a flora comparable to that now existing in 

 Northern Germany, justify geologists in concluding that the inter- 

 glacial epoch was one of long duration, and characterized in 

 Germany by climatic conditions apparently not less temperate 

 than those that now obtain. One of the phases of that inter- 

 glacial epoch, as we have seen, was the overflowing of the Baltic 

 provinces by the waters of the North Sea. 



4. To this well-marked interglacial epoch succeeded another 

 epoch of arctic conditions, when the Scandinavian inland ice 



H. ichroder, Jahii\ d. k.preuss. gccl. Landesanstalt fiir 1887, p. 360, 



