THE ORIGIN OF THE HUMAN BODY 289 



reduction of the left hand, or overdevelopment of the right 

 hand, resulting from this racial practice. "The superiority of 

 one hnnd," says G. Elliot Smith, "is as old as mankind." 

 (Smithson. Inst. Rpt. for 1912, p. 570.) It is true that only 

 about 6,000 years of human existence are known to history, 

 but, if one accepts the most conservative estimates of glaci- 

 ologists, man has had a much longer prehistory, the lowest 

 estimates for the age of man being approximately 30,000 years. 

 Thus W. J. Sollas tells us that the Glacial period, in which 

 man first appeared, came to an end about 7,000 years ago, 

 and that the men buried at Chapelle-aux-Saints in France 

 lived about 25,000 years ago. His figures agree with those of 

 C. F. Wright, who bases his calculations on the Niagara 

 Gorge. The Niagara River is one of the postglacial streams, 

 and the time required to cut its gorge has been calculated as 

 7,000 years. Gerard De Geer, the Swedish scientist, gives 

 20,000 years ago as the end of glacial and the commencement 

 of recent or postglacial time. He bases his estimates on the 

 sediments of the Yoldia Sea in Sweden. His method consists 

 in the actual counting of certain seasonally-laminated clay 

 layers, presumably left behind by the receding ice sheet of the 

 continental glacier. The melting is registered by annual depo- 

 sition, in which the thinner layers of finer sand from the 

 winter flows alternate with thicker layers of coarser material 

 from the summer flows. In warm years, the layers are thicker, 

 in colder years they are thinner, so that these laminated 

 Pleistocene clays constitute a thermographic as well as a 

 chronological record. De Geer began his study of Pleistocene 

 clays in 1878, and in 1920 he led an expedition to the United 

 States, for the purpose of extending his researches. (Of. Science, 

 Sept. 24, 1920, pp. 284-286.) At that time, he claimed to have 

 worked out the chronology of the past 12,000 years. His 

 figure of 20,000 years for postglacial time, while very displeas- 

 ing to that reckless foe of scientific caution and conservatism, 

 Henry Fairfield Osbom, tallies very well with the estimates 

 of Sollas and Wright. H. Obermaier, basing his computation 



