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.