490 



NATURE 



\Sept. 19, 1889 



We are reminded by Klockmann (jfahrb. d. k. preuss. 

 geol. Landesanstalt fiir 1883, p. 262) and Wahnschaffe 

 \op. cit., and Zcilschr. d. deuisch. geol. Ges. 1886, p. 367) 

 that the inland ice must have acted as a great dam, and that 

 wide areas in Germany, &c., would be flooded, partly by water 

 derived from the melting inland ice, and partly by waters flowing 

 north from the hilly tracts of Middle Germany. In the great 

 basins thus formed there would be a commingling of fine silt- 

 material derived from north and south, which would necessarily 

 come to form a deposit having much the same character 

 throughout. 



Fiom what I have myself seen of the Kiss in various parts of 

 Germany, and from all that I have gathered from reading 

 and in conversation with those who have worked over loss- 

 covered region;*, 1 incline to the opinion that loss is for the most 

 part of aqueous origin. In many cases this can be demonstrated, 

 as by the occurrence of bedding and the intercalation of la3ers of 

 .stones, sand, gravel, &c., in the deposit; again, by the not in- 

 frequent appearance of fresh-water shells ; but, perhaps, chiefly 

 by the remarkable uniformity of character which the loss itself 

 displays. It seems to me reasonable al.-o to believe that the 

 flood -waters of glacial times must needs have been highly charged 

 with finely-divided sediment, and that such sediment would be 

 spread over wide regions in the low grounds — in the slack-waters 

 of the great rivers, and in the innumerable temporary lakes which 

 occupied, or partly occupied, many of the valleys and depressions 

 of the land. There are different kinds of loss or loss like 

 deposits, however, and all need not have been formed in the 

 same way. Probably some may have been derived, as Wahn- 

 schafTe has suggested, from the denudation of boulder-clay. 

 Possibly, also, some loss may owe its origin to the action of rain 

 upon the stony clays, producing what we in this country would 

 call "rain-wash." There are other accumulations, however, 

 which no aqueous theory will satisfactorily explain. Under this 

 category comes much of the so-called Bergloss, with its abundant 

 land-shells, and its generally unstratified character. It seem-; 

 likely that such loss is simply the result of sub-aerial action, and 

 owes its origin to rain, frost, and wind acting upon the superficial 

 formations, and rearranging their finer-grained constituents. And 

 it is quite possible that the upper portion of much of the loss of 

 the lower grounds may have been re-worked in the same way. 

 But I confess I cannot yet find in the facts adduced by German 

 geologists any evidence of a dry-as-dust epoch having obtained 

 in Europe during any stage of the Pleistocene period. The geo- 

 graphical position of our continent seems to me to forbid the 

 possibility of such climatic conditions, while all the positive 

 evidence we have points rather to humidity than dryness as the 

 prevalent feature of Pleistocene climates. It is obvious, however, 

 that after the flood-waters had disappeared from the low grounds 

 of the Continent, sub-aerial action would come into play over the 

 wide regions covered by glacial and fluvio-glacial deposits. Thus, 

 in the course of time, these deposits would become modified, — 

 just as similar accumulations in these islands have been top- 

 dressed, as it were, and to some extent even rearranged. I am 

 strengthened in these views by the conclusions arrived at by 

 M. Falsan, the eminent French glacialist. Covering the plateaux 

 of the Dombs, and widely spread throughout the valleys of the 

 Rhone, the Ain, the Isere, &c., in France, there is a deposit of 

 loss, he says, which has been derived from the washing of the 

 ancient moraines. At the foot of the Alps, where black schists 

 are largely developed, the loss is dark grey ; but west of the 

 secondary chain the same deposit is yellowish, and composed 

 almost entirely of siliceous materials, with only a very little car- 

 bonate of lime. 'J his Union or loss, however, is very generally 

 modified towards the top by the chemical action of rain, the 

 yellow loss acquiring a led colour. Sometimes it is crowded 

 with calcareous concietions; at other times it has been deprived 

 of its calcareous element and convert* d into a kind of pulverulent 

 silica or quartz. This, the true loss, is distinguished from another 

 Icliiii, w hich Falsan recognizes as the product of atmospheric action 

 — foimed, in fact, in place, from the disintegration and decom- 

 position of the subjacent rocks. Even this hhni has been modified 

 by running water — dispersed or accumulated locally, as the case 

 may be (Falsan, " La Periode glaciaire," p. 81). 



All that we know of the loss and its fossils compels us to in- 

 clude this accuii.ulation as a product of the Pleistocene period. 

 It is not of postglacial age — even much of what one may call the 

 "remodified loss" being of Late Glacial or Pleistocene age. I 

 cannot attempt to give here a summary of what has been learned 

 within recent years as to the fauna of the loss. The researches 



of Nehring and Liebe have familiarized us with the fact that at 

 some particular stage in the Pleistocene period a fauna like that 

 of the alpine steppe- lands of Western Asia was indigenous to 

 Middle Europe, and the recent investigations of Woldrich have 

 increased our knowledge of this fauna. At what horizon, then, 

 does this steppe-fauna make its appearance? At Thiede, Dr. 

 Nehring discovered in so-called loss three successive horizons, 

 each characterized by a special fauna. The lowest of these faunas 

 was decidedly arctic in type; above that came a steppe-fauna, 

 which last was succeeded by a fauna comprising such forms as 

 mammoth, woolly rhinoceros. Bos, Cervits, horse, hyaena, and 

 lion. Now, if we compare this last fauna with the forms which 

 have been obtained from true postglacial deposits —those deposits, 

 namely, which overlie the younger boulder-clays and flood-accu- 

 mulations of the latest glacial epoch — we find little in common. 

 The lion, the mammoth, and the rhinoceros are conspicuous by 

 their absence from the postglacial beds of Europe. In place of 

 them we meet with a more or less arctic fauna, and a high-alpine 

 and arctic flora, which, as we all know, eventually gave place to 

 the flora and fauna with which Neolithic man was contem- 

 poraneous. As this is the case throughout North-Western and 

 Central Europe, we seem justified in assigning the Thiede beds 

 to the Pleistocene period, and to that interglacial stage which 

 preceded and gradually merged into the last glacial epoch. That 

 the steppe-fauna indicates relatively drier conditions of climate 

 than obtained when perennial snow and ice covered wide areas 

 of the low ground goes without saying ; but I am unable to agree 

 with those who maintain that it implies a dry- as dust climate, 

 like that of some of the steppe-regions of our own day. The 

 remarkable commingling of arctic and steppe-faunas discovered 

 by Woldrich in the Bohmerwald {Silzungsb. d. kais. Akad. d. 

 IV. math. nat. CI., 1880, p. 7; 1881, p. 177; 1883, p. 978) 

 shows, I think, that the jerboas, marmots, and hamster- 

 rats were not incapable of living in the .'■ame regions contem- 

 poraneously with lemmings, arctic hares, Siberian social voles, 

 &c. But when a cold epoch was passing away the steppe-forms 

 piobably gradually replaced their arctic congeners, as these 

 migrated northwards during the continuous amelioration of the 

 climate. 



If the student of the Pleistocene faunas has certain advantages 

 in the fact that he has to deal with forms many of which are 

 still living, he labours at the same time under disadvantages 

 which aie unknown to his colleagues who are engaged in the 

 study of the life of far older periods. The Pleistocene period 

 was distinguished above all things by its great oscillations of 

 climate — the successive changes being repeated, and producing 

 correlative migrations of floras and faunas. We know that 

 arctic and temperate faunas and floras flourished during inter- 

 glacial times, and a like succession of life-forms followed the 

 final disappearance of glacial conditions. A study of the organic 

 remains met with in any particular deposit will not necessarily, 

 therefore, enable us to assign these to their proper horizon. The 

 geographical position of the deposit, and its relation to Pleisto- 

 cene accumulations elsewhere must clearly be taken into account. 

 Already, however, much has been done in this direction, and it 

 is probable that ere long we shall be able to arrive at a fair 

 knowledge of the various modifications which the Pleistocene 

 floras and faunas experienced during that protracted period of 

 climatic changes of which I have been speaking. We shall even 

 possibly learn how often the arctic, steppe-, prairie-, and forest- 

 faunas, as they have been defined by Woldrich, replaced each 

 other. Even now some approximation to this better knowledge 

 has been made. Dr. Pohlig,^ for example, has compared the 

 remains of the Pleistocene faunas obtained at many different 

 places in Europe, and has presented us with a classification 

 which, although confessedly incomplete, yet serves to show the 

 direction in which we must look for further advances in this 

 department of inquiry. 



J luring the last twenty years the evidence of interglacial con- 

 ditions both in Europe and America has so increased that geo- 

 logists generally no longer doubt that the Pleistocene period was 

 characterized by great changes of climate. The occurrence at 

 many difierent localities on the Continent of beds of lignite and 

 fresh-water alluvia, containing remains of Pleistocene Mammalia, 

 intercalated between separate and distinct boulder-clays, has 



^ Pohl'g, Sitzungsb. d. Niederrheiniicheu Gcsellschaft zu Bonn, 1884 ; 

 Zeitschr. d. deiitsch. geoiog. Ges., 1887, p 798. For a very full account 

 of the diluvial European and Northern Asiatic mammalian faunas by Wold- 

 rich, see i\Ieiii. dc I'Acatt. des Sciences de St. Petersbourg, Ser. vii , t. 



