INVESTIGATION VERSUS PROPAGANDISM 311 



marked off naturally by the successive ice invasions and retreats, 

 because these very profoundly affected all the life in the middle 

 and northern latitudes of the Eastern and Western hemispheres, 

 while indirectly they greatly influenced the life-conditions in the 

 more southerly latitudes. 



Though these new physico-dynamic criteria do not afford very 

 sharp lines of demarcation, they are in reality sharper than the 

 paleontological criteria they have replaced. Changes of species 

 are slower, and their interpretation more uncertain, than the 

 changes in the great ice-sheets. It will help to show the real 

 significance of the diverse interpretations of the Vero case if we 

 here give a table of the relative dates of the several glacial stages 

 compiled from estimates made by the more experienced students 

 of glacial phenomena. Of course these are by no means final figures ; 

 they are held subject to very considerable changes as additional 

 data are gathered; but they may be regarded as indicating tenta- 

 tively the order of magnitude of the time-distribution of the glacial 

 stages. We have derived from the compiled estimates what seem 

 to us conservative minimum estimates. 



ESTIMATED TIME-STAGES OF THE PLEISTOCENE PERIOD 



Compiled Estimate Minimum Estimate 



Close of Pleistocene, beginning of Recent 25,000 yrs. ago 20,000 yrs. ago 



Climax of Late Wisconsin glacial stage . . 40,000 " " 30,000 " " 



Climax of Early Wisconsin glacial stage . 95,000 " " 60,000 " " 



Middle of Peorian interglacial stage 135,000 " " 90,000 " " 



Climax of lowan glacial stage 180,000 " " 105,000 " " 



Middle of Sangamon interglacial stage . . 260,000 " " 155,000 " " 



Climax of Illinoisan glacial stage 340,000 " " 190,000 " " 



Middle of Yarmouth interglacial stage . . 500,000 " " 275,000 " " 



Climax of Kansan glacial stage 660,000 " " 330,000 " " 



Middle of Aftonian interglacial stage. . . . 900,000 " " 450,000 " " 



Climax of Jerseyan glacial stage 1,200,000 " " 540,000 " " 



Maximum estimates should probably be double the compiled 

 estimates in the later stages and more than double in the earlier 

 stages. 



Now, if we take the extreme ages to which the fossils at Vero 

 have been referred by different members of the conferences, the 



