GLACIAL GEOLOGY. 227 



loess, is distinguished from another, lehni, which Falsan recognizes as 

 the product of atmospheric action, formed, in fact, in place from the 

 disintegration and decomposition of the subjacent rocks. Even this 

 lehm has been modified by running water, dispersed or accumulated 

 locally, as the case may be.* 



All that we know of the loess and its fossils compels us to include this 

 accumulation as a product of the Pleistocene period. It is not of post- 

 glacial age, even much of what one may call the "remodifled loess" 

 being of Late Glacial or Pleistocene age. I can not attempt to give 

 here a summary of what has been learned within recent years as to the 

 fauna of the loess. Th(3 researches of Xehriug and Liebe have familiar- 

 ized us with the fact that at some particular stage in the Pleistocene 

 period a fauna like that of the alpine steppe lauds 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 fauua make its appearance "? At Thiede Dr. Nehring 

 discovered in so-called loess 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, 

 Gervus, horse, hyiBua, and lion. Xow, if we compare this last fauua 

 with the forms which have been obtained from true postglacial deposits, 

 those dei)osits, namely, which overlie the younger bowlder clays and 

 flood accumulations 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 contemporaneous. As this 

 is the case throughout northwestern and central Europe, we feel. justi- 

 fied in assigning the Thiede beds to the Pleistocene period, and to that 

 interglacial stage which preceded and gradually merged into the last 

 glacial epoch. - - - 



If the student of the Pleistocene fauna has certain advantages in the 

 fact that he has to deal with forms many of which are still living, he 

 labors at the same time under disadvantages which are 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 interglacial 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, there- 

 fore, enable us to assign these to their proi)er horizon. The geograph- 



* Falsau ; £a Pe'riode (jlaciaire, p. 81. 



