ANTIQUITY OF THE PILTDOWN RACE 307 
the same geological age " as the Heidelberg mandible — 
the oldest human remains yet found on the continent of 
Europe. The geological age of the Heidelberg mandible, 
as we have seen in a former chapter, has been accurately 
fixed. It was discovered in a deposit laid down in the 
ancient bed of a tributary of the Neckar not long after 
the l^leistocene stage of the earth's history was well begun. 
The Cromer beds were in process of formation in East 
Anglia. Dr Smith Woodward's opinion, then, is that the 
Piltdown form of man was living in Southern England 
at an early part of the Pleistocene period, and that, at 
the same date, a very different kind of man was inhabiting 
Central Europe. 
The reader mi*iy naturally break in with the question : 
How long ago is that ? The facts which will yield an 
estimate of geological time certainly exist, and in the 
opinion of men like Rutot, Sollas, and Penck are sufficient 
to afford an approximate estimate — the first step towards 
accurate figures. We shall take the estimate of Professor 
Sollas ^ first. He regards the deposits which were laid 
down during the Pleistocene period as forming, when 
superimposed, a thickness or depth of 4000 feet (see 
frontispiece). He estimates that the formation has pro- 
ceeded at the rate of a foot per century, and that there- 
fore the collective deposits of the Pleistocene period 
probably have taken about four hundred thousand years 
to form. The estimate given by Professor Rutot is much 
less — one hundred and forty thousand years. Short as 
it is, that estimate deserves our serious consideration, for 
it is founded on a prolonged study of the Pleistocene 
formations found along the river valleys of Belgium. 
There is a third estimate which must also weigh with us 
in coming to a conclusion as regards the duration of 
the Pleistocene period — that of Professor Penck. '^ He 
has studied the changes produced by Alpine glaciers dur- 
ing the Pleistocene cycles of extreme cold. He is of 
opinion that such changes indicate for the Pleistocene 
* Nature, 1900, vol Ixii. p. 481. 
^ See A. Penck, Zeitschriftfiir Ethnologic, 1908, \ol. xl. p. 390. 
