232 PROFESSOR JAMES GEIKIE, LL.D., D.C.L., F.R.S., ETC., ON 



changes similar to those that marked the accumulation of the 

 river-deposits of the Thames, the Seine, etc. Of younger 

 date than the Mosbach Sands is another series of unfossilifer- 

 ous gravels, which, like the older series, are charged with ice- 

 floated erratics. The beds at Mosbach are thus shown to 

 be of interglacial age : they occupy the same geological 

 horizon as the interglacial beds of Switzerland and other 

 glaciated tracts in Central and Northern Europe. 



To this position must likewise be assigned the Pleistocene 

 river-alluvia of other districts. There is no other horizon, 

 indeed, on which these can be placed. That they are not of 

 postglacial age is shown by the fact that in many places the 

 angular gravels and flood-loams of the glacial period overlie 

 them. And that they cannot all belong to preglacial times 

 is proved by the frequent occurrence underneath them of 

 glacial or fluvio-glacial accumulations. It is quite possible, of 

 course, that here and there in the valleys of Western and 

 Southern Europe some of the Pleistocene alluvia may be of 

 preglacial age. But in the main these alluvia must be 

 regarded as the equivalents of the glacial and interglacial 

 deposits of northern and alpine districts. This will appear 

 a reasonable conclusion when Ave bear in mind that long 

 before the Pliocene period came to a close the climate 

 of Europe had begun to deteriorate. In England, as we 

 know, glacial conditions supervened almost at the advent 

 of the Pleistocene period. And the same was the case in the 

 alpine lands of the south. Again, in the glaciated areas of 

 north and south alike, the closing stage of the Pleistocene 

 was characterized by cold climatic conditions. And thus in 

 those regions the glacial and interglacial epochs were co- 

 extensive with that period. It follows, therefore, that the 

 Pleistocene deposits of extra-glacial areas must be the equi- 

 valents of the glacial and interglacial accumulations else- 

 where. If we refused to admit this we should be puzzled 

 indeed to tell what the rivers of Western and Southern 

 Europe were doing throughout the long-continued glacial 

 period. There is no escape from the conclusion that the 

 Pleistocene river-alluvia and cave- accumulations must be 

 assigned to the same general horizon as the glacial and 

 interglacial deposits. This is now admitted by continental 

 paleontologists who find in the character of Pleistocene 

 organic remains abundant proof that the old river-alluvia and 

 cave-accumulations were laid down under changing climatic 

 conditions. Did neither glacial nor interglacial deposits 



