वेदों की प्राचीनता एवं काल-निर्णय / ओरायन (लोकमान्य बाल गंगाधर तिलक - खगोलीय वैदिक शोध)

PREHISTORIC TIMES. 13
But these estimates are not better than mere approximations,
and generally speaking we may take the Neolithic age in Europe
as commencing not later than 5000 B. C.
But when we pass from the Neolithic to the Palæolithic
period the difficulty of ascertaining the commencement of the
latter becomes still greater. In fact we have here to ascertain
the time when the Post-Glacial period commenced. The
Palæolithic man must have occupied parts of Western Europe
shortly after the disappearance of the Ice Age and Prof. Geikie
considers that there are reasons for supposing that he was inter-
glacial. The Glacial period was characterised by geographical
and climatic changes on an extensive scale. These changes and
the theories regarding the cause or the causes of the Ice Age will
be briefly stated in the next chapter. We are here concerned
with the date of the commencement of the Post-Glacial period,
and there are two different views entertained by geologists on the
subject. European geologists think that as the beginning of the
Post-Glacial period was marked with great movements of eleva-
tion and depression of land, and as these movements take place
very slowly, the commencement of the Post-Glacial period cannot
be placed later than 50 or 60 thousand years ago. Many American
geologists, on the other hand, are of opinion that the close of the
last Glacial period must have taken place at a much more recent
date. They draw this inference from the various estimates of time
required for the erosion of valleys and accumulation of alluvial
deposits since the last Glacial period. Thus according to Gilbert,
the post-glacial gore of Niagara at the present rate of erosion
must have been excavated within 7000 years ¹. Other American
geologists from similar observations at various other places have
arrived at the conclusion that not more than about 8000 years have

1. See Geikie's Fragments of Earth Lore, p. 286; also Dr. Bonney's.
   Story of our Planet, p. 560.