372 SECTIONAL TRANSACTIONS.—C. 
Prof. H. Fairrretp Osporn.—New estimates of the Length of Pleistocene 
Time and Means of dating the Stone Age Man by the Elephant-Enamel 
Method. 
The more or less perfect grinding teeth of fossil elephants have been found in 
association with human remains or implements from the first period of archzological 
discovery. These human fossils have been more or less roughly dated by the fossil 
elephants and other mammals with which they have been discovered, but quite 
recently the means has been found of making this dating much more precise. In 
brief, the enamel composing the ridge plates of the elephant grinders may now be 
very accurately measured, and to each human type may be assigned a precise elephant 
or stegodont enamel length. This new method of dating various stages of fossil men 
may be called ganomeiric. The minimum enamel length in an elephant is the upper 
Pliocene 825 mm.; the maximum enamel length is the upper Pleistocene 7,300 mm. 
in one elephant, and 9,700 mm. in another. The maximum enamel length in the 
stegodonts is far below that attained by the elephants. 
This ganometric method may be combined with the most recent estimates of 
Pleistocene time based chiefly on the glaciological work of Leverett, and of de Geer 
and his former associate Antevs, who worked in the glaciated lamin of Sweden and 
of the coast of New England. These results are put together for the present com- 
munication by Dr. Chester A. Reeds of the American Museum, as follows :-— 
‘Tn general the early time estimates of Penck and Bruckner, in which 500,000 years 
are assigned to the glacial epoch, have been doubled to 1,000,000 years—a time 
extension in full accord with the remarkable evolution and migrations during this 
closing period of the Age of Mammals. F’. Leverett, glaciologist of the U.S. Geological 
Survey, in a 1930 paper discusses the relative length of glacial and interglacial stages 
in America during Pleistocene time ; he concludes that the entire epoch must have 
been 1,000,000 years in length, and that of this time 300,000 years were glacial and 
700,000 years interglacial. He assumes that the glacial periods I-IV were of equal 
duration, 75,000 years each, and estimates interglacial 3 stage, the Sangamon Peorian, 
at 50,000 years, thus leaving 650,000 years to be divided between interglacial 2 and 
interglacial 1. In a revised classification of the Pleistocene soon to be published, 
entitled “The Classification and Duration of the Pleistocene Period,’ four epochs 
(series) will be introduced by Kay, the youngest of which will be the Eldoran.’ 
These results are presented in a chart 10 metres in length, in which the whole of 
Pleistocene time is subdivided into hundreds of thousands and tens of thousands of 
years. ‘To the left of the chart the closing stage of 250,000 years of Pliocene time is 
added. To the right of the chart is added the 40,000 years of post-Pleistocene and 
recent time. 
Superposed upon the chart are the duration periods of six of the independent lines 
of fossil Proboscidians, and the total enamel length attained in the evolution of the 
3rd superior molars in each of these lines, namely :— 
Glaciation IV. , 3 é . 80,000 Mammonteus primigenius. 
3d Interglacial . : . : - 110,000 Palwoloxodon germanicus. 
Glaciation II] . ‘ 5 : . 90,000 
2d Interglacial . : ‘ z . 330,000 Parelephas trogontherit. 
Glaciation IT. : , . . 90,000 
. { Archidiskodon meridionalis. 
lst Interglacial . é 3 : . 220,000 | Paloloxodon antiquus. 
Glaciation I 3 3 . : . 80,000 Mammonteus astensis. 
Total . : : 1,000,000 
As each of these elephants has its own duration period we are enabled to calculate 
the rate of evolution of the enamel plates in each phylum or line of descent as follows :— 
Average Ganometric Evolution per 10,000 years 
Archidiskodon, based on A. imperator ; = 5 : -. 154 mm. 
Parelephas, based on P. progressus . : ‘ = : asim me: 
Mammonteus, based on M. primigenius . : ; j . 40mm. 
Paleoloxodon, based on P. ant. italicus . : ; : . 43 mm. 
Loxodonta, based on L. africana. ; : : t . 20mm. 
Elephas, based on EH. indicus . 5 ; : : ‘ . 60 mm. 
~P,~ ¥. 
