10 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. 



Sir Archibald Geikie's estimate was 100 million of years. 



Professor J. D. Dana's estimate was 48 million of years. 



Professor Joseph Le Conte's estimate was 30 million of years. 



Mr. C. D. Walcott's estimate was 28 million of years for the 

 total period of existence of fossil-bearing sediments. 



And for the time which has elapsed since the earth was in a 

 molten state the following eminent physicists drew these con- 

 clusions : 



Sir William Thomson's estimate was 100 million years. 



Professor George H. Darwin's estimate was 57 million j^ears. 



Professor Simon Newcomb's estimate was 14 million years. 



Dr. Alexander Winchell's estimate was 3 million years. 



As to the relative durations of the greater geological time 

 divisions the conclusions of eminent scientists are more in ac- 

 cord. 



For the Paleozoic (Ancient Life), which includes the Silurian, 

 Devonian and Carboniferous Ages, seventeen million, five hun- 

 dred thousand years. 



The Mesozoic or Mediaeval (Age of Keptiles), seven million 

 tAvo hundred and forty thousand years: and for the Cenozoic 

 or Recent, which is represented by the Tertiary and Post-Ter- 

 tiary Periods, two million nine hundred thousand years. 



' ' The time since the departure of the ice of the Glacial period 

 from this portion of the continent has been estimated by several 

 eminent authorities, from different data, and their figures fall 

 within six thousand to ten thousand years." * 



Prehistoric Man and his Development*. 



BY DR. LORENZO G. YATES, F. L. S. 



Honorary Member Southern California Academy of Sciences, 

 President of the Santa Barbara Societj' of Natural Hitory. Etc. 



History is defined as a narrative of past events, oral or writ- 

 ten, and is divided into Ancient, Mediaeval and Modern. An- 

 cient History treats of the history of man from the earliest rec- 

 ords to the destruction of the Roman Empire, A. D. 476; Me- 

 diaeval History is the historj^ of the Middle Ages, from A. D, 

 476 to the beginning of the sixteenth century, and Modern 

 History from the close of the Middle Ages to the present time. 



As the above terms apply to the world at large and man in 

 general the study of the history of man as considered in his re- 



* Herman LeEoy Fairchild, in Proceedings of the Eochester Acad- 

 emy of Science, Vol. II. 



