CONCLUSION. 559 



of Neolithic man in Europe must date back far beyond fifty or 

 seventy centuries. 



Although I am not prepared to give a more or less definite 

 date for the beginning of the Later Prehistoric Period, I am far 

 from thinking that a greater definiteness will not some day be 

 attained. All the chronometers which have hitherto been 

 appealed to by geologists are somewhat misleading, for we 

 cannot assume that peat, alluvia, and other strata, have attained 

 their present thickness at the same rate as they are now accreting. 

 The climatic changes of the past must likewise be taken into 

 our calculations, and the precise effect of these it will always be 

 a hard matter to compute. But until this is done our results 

 must be inadequate and incomplete. Whilst readily admitting 

 that the methods employed by Morlot and others are of the 

 greatest value, and have given a precision to our conceptions of 

 the antiquity of archaeological periods, which was previously 

 wanting, I confess that it is rather to the astronomer and the 

 physicist than to the geologist that I look for assistance in 

 ascertaining the more precise chronology we are in search of. 

 Continued study of Glacial and Postglacial deposits has deepened 

 my conviction that the theory advanced by my friend and 

 colleague Dr. Croll contains the secret of the whole matter. 

 This theory gives an adequate explanation of that great alter- 

 nation of cold and genial climates which obtained during the 

 Pleistocene or Glacial Period, and enables us to fix the date of 

 the Ice Age with as much exactness as we can ever hope to 

 attain. If it be true, then, that the Pleistocene era corresponded 

 with the latest period of excessive eccentricity of the earth's 

 orbit, it follows that the beginning of the Palaeolithic Age 

 must go back some 200,000 years ago ; nor to those who are 

 adequately acquainted with the vast changes which supervened 

 during Glacial and Interglacial times will such an antiquity 

 appear extravagant. On the contrary, many geologists, looking 

 at the enormous results that accrued from the action of the 

 denuding forces in the Pleistocene Period, have been inclined to 

 assign even a higher date to the commencement of the Ice Age. 



