WHOLE VOL. SKELETAL REMAINS OF EARLY MAN HRDLICKA 1 3 



definite and well-known time standards. Sensible of the need, geol- 

 ogists, paleontologists, and prehistorians have for a long time es- 

 sayed, through the study of erosions and deposits, of the reduction 

 changes in the radio-active elements, of the salt content of the 

 seas, etc., to arrive at such estimates for all geological time* and for 

 the Glacial Age in particular. But the results differ so widely that 

 they are of little utility. Thus the estimates of the duration of the 

 Ice Age range from 200,000 (or 250,000 if the first glaciation is in- 

 cluded) years by Keith,' to 1,000,000 years by Osborn.^ The esti- 

 mates for the human periods by these two well qualified authorities 

 are placed here side by side. They show the uncertainties of the case 

 among even the foremost students of the question. To some of the 

 American geologists {e.g., Rollin Chamberlin) the duration of the 

 Ice Age appears even greater than estimated by Osborn. 



Conditions are incomparably better, as has already been mentioned, 

 for the time since the maximum of the latest glaciation. Thanks 

 especially to the painstaking researches of De Geer and Antevs, who 

 in addition to other original work have studied the stratified glacial 

 clays in Scandinavia and America, we now know that the length of 

 time elapsed since the cold of the last glacial invasion had reached 

 its maximum amounts close to 35,000 years. 



This datum is exceedingly valuable to human prehistory for it 

 corresp^onds to the latest part of the Mousterian or Neanderthal 

 period of man. The settling of this date, if fully corroborated by 

 future research, establishes a substantial and most important mile- 

 stone of human chronology, for it clears up the problem of the placing 

 and collective duration of all the following paleolithic cultures, which 

 comprise the Aurignacian, Solutrean and Magdalenian. 



A compounding of the various estimates, together with individual 

 studies, has led me to the tentative chronology shown in the follow- 

 ing table, the value of which is merely that of a plausible approxi- 

 mation. 



* See especially a symposium on The Age of the Earth, by T. C. Chamberlin, 

 J. M. Clarke, E. W. Brown, and W. Duane. Proc. Amer. Philos. Soc, Vol. 61, 

 pp. 247-288, 1922; with further references. Reprinted Smithsonian Ann. Rep. 

 for 1922, pp. 241-273, 1924. 



* Keith, Sir Arthur, The Antiquity of Man. 3d ed., 2 Vols., London, 1927. 



* Osborn, Henry Fairfield, Our Ancestors Arrive in Scandinavia. Nat. Hist., 

 Vol. 22, pp. 1 17-134, New York, 1922; also in Man Rises to Parnassus, p. 106, 

 Princeton, 1927. 



