228 GLACIAL GEOLOGY. 



ical position of the deposit and its relation to Pleistocene 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 modifi- 

 cations which the Pleistocene floras and faunas experienced during 

 the protracted period of climatic changes of which 1 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. 



During the last twenty years the evidence of interglacial conditions 

 both in Europe and America has so increased that geologists generally 

 no longer doubt that the Pleistocene period was characterized by great 

 changes of climate. The occurrence at many different localities on the 

 continent of beds of lignite and fresh-water alluvia, containing remains 

 of Pleistocene mammalia, intercalated between separate and distinct 

 bowlder clays, has left us no alternative. Tbe interglacial beds of the 

 Alpine lands of Central Europe are paralleled by similar deposits in 

 Britaiu, Scandinavia, (Germany, and France. But opinions differ as to 

 the number of glacial and interglacial epochs, many holding that we 

 have evidence of only two cold stages and one general interglacial 

 stage. This, as I have said, is the view entertained by most geologists 

 who are at work on the glacial accumulations of Scandinavia and North 

 Germany. On the other hand, Dr. Penck and others, from a study of 

 the drifts of the German alpine lands, believe that they have met with 

 evidence of three distinct epochs of glaciation and two epochs of iuter- 

 glacial conditions. In France, while some observers are of opinion 

 that there have been only two epochs of general glaciation, others, as 

 for example, M. Tardy, find what they consider to be evidence of 

 several such epochs. Others again, as M. Falsao, do not believe in the 

 existence of any interglacial stages, although they readily admit that 

 there were great advances and retreats of the ice during the glacial 

 period. M. Falsan, in short, believes in oscillatious, but he is of the 

 opinion that these were not so extensive as others maintained. It is, 

 therefore, simply a question of degree, and whether we speak of oscilla- 

 tions or of epochs we must needs admit the fact that through all the 

 glaciated tracts of Europe fossiliferous deposits occur intercalated 

 among glacial accumulations. The successive advance and retreat of 



*Poblig: Sitzungsb. d. Niederrheinischen GeselUchaft zii Bonv, 1884: Zeitschr.d. deutsch. 

 geolog. Ges., 1887, p. 798. For a very full account of the diluvial Europeau aud 

 Northern Asiatic mammalian faunas by AVoUlricIj, see Mem. dc I'Jcad. des Sciences de 

 St.-1'eteisbourg, 1887, 7'' s6r., tom. xxxv. 



