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

THE GLACIAL PERIOD. 21 that in the distant geological ages the climate of our planet must have been characterised by similar rotations of hot and cold seasons. But such a supposition is directly contradicted by geological evidence. The inclination of the earth's axis to the plane of the ecliptic, or what is technically called the obliquity of the ecliptic, is not the sole cause of climatic variations on the surface of the globe. High altitude and the existence of oceanic and aerial currents, carrying and diffusing the heat of the equatorial region to the other parts of the globe, have been found to produce different climates in countries having the same latitude. The Gulf Stream is a notable instance of such oceanic currents, and had it not been for this stream the climate in the North-West of Europe would have been quite different from what it is at present. Again, if the masses of land and water be differently distributed from what they are at present, there is every reason to suppose that different climatic conditions will prevail on the surface of the globe from those which we now experience, as such a distribution would materially alter the course of oceanic and aerial currents going from the equator to the Poles. Therefore, in the early geological ages, when the Alps were low and the Himalayas not yet upheaved, and when Asia and Africa were represented only by a group of islands, we need not be surprised if, from geological evidence of fossil fauna and flora, we find that an equable and uniform climate prevailed over the whole surface of the globe as the result of these geographical conditions. In Mesozoic and Cainozoic times this state of things appears to have gradually changed. But though the climate in the Secondary and the Tertiary era was not probably as remarkably uniform as in the Primary, yet there is clear geological evidence to show that until the close of the Pliocene period in the Tertiary era the climate was not yet differentiated into zones and there were then no hot and cold extremes as at present. The close