CONCLUSION. 



557 



the scope of this inquiry, nor do I take cognisance of the many 

 modifications which have been produced by recent volcanic 

 action, the denuding force of waves and currents, and the growth 

 of deltas upon the outline of the land within historical times. 

 All these have conspired to bring about the present climatic and 

 geographical conditions of our continent; and to so great an 

 extent is this the case, that it is often extremely hard, or even 

 impossible, to assign to each factor its proper share in the result 

 produced. At present we seem to be living in a comparatively 

 dry epoch — but the appearances that lead to this conclusion 

 are not improbably due in no small measure to the drainage- 

 operations of the husbandman. 



It will be noted that our knowledge of postglacial climatic 

 changes is derived chiefly from an examination of the post- 

 glacial accumulations of North-western Europe. This arises 

 from the circumstance that such mutations must necessarily 

 have been most marked in the higher latitudes. Farther to the 

 south they would become less and less appreciable, just as in 

 Pleistocene times the contrast between glacial and interglacial 

 conditions must have been less pronounced in southern than in 

 northern regions. 



Hitherto I have said nothing as to the absolute duration of 

 the Pleistocene and the Postglacial Periods. The phenomena 

 described leave us in no doubt that an immense lapse of time 

 intervened between the appearance and disappearance of Palaeo- 

 lithic man, and the changes which took place during the Post- 

 glacial Period likewise demand considerable time for their 

 evolution. Within recent years several attempts have been 

 made to estimate the dates of the Neolithic and later Ages, and 

 the results obtained are interesting and suggestive. Thus, M. 

 Morlot has shown that the cone of alluvium and detritus brought 

 down by the torrent of the Tiniere to the Lake of Geneva at 

 Villeneuve, and of which an admirable section was exposed in 

 the railway-cutting, exhibits three distinct and superposed layers 

 of vegetable soil or old land-surfaces, which are separated from 

 each other by a variable depth of detritus. The uppermost 



