It appears almost certain, therefore, that some intermediate position of the axis would be the most favourable; and that which actually exists seems to combine the advantage of change of seasons with good climatical conditions over the largest possible area. We know that during the greater part of the epoch of life-development this area was much greater than at present, since a luxuriant vegetation of deciduous and evergreen trees and shrubs extended up to and within the Arctic Circle, leading to the formation of coal-beds both in palæozoic and tertiary times; the extremely favourable conditions for organic life which then prevailed over so large a portion of the globe's surface, and which persisted down to a comparatively recent epoch, lead to the conclusion that no more favourable degree of obliquity was possible than that which we actually possess. A short account of the evidence on this interesting subject will now be given. PERSISTENCE OF MILD CLIMATES THROUGH GEOLOGIC TIME The whole of the geological evidence goes to show that in remote ages the climate of the earth was generally more uniform, though perhaps not warmer, than it is now, and this can be best explained by a slightly different distribution of sea and land, which allowed the warm waters of the tropical oceans to penetrate into various parts of the continents (which were then more broken up than they are now), and also to extend more freely into the Arctic regions. So soon as we go back into the tertiary period, we find indications of a warmer climate in the north temperate zone; and when we reach the middle of that period, we find abundant indications, both in plant and animal remains, of mild climates near to the Arctic Circle, or actually within it. On the west coast of Greenland, in 70° N. lat., there are found abundance of fossil plants very beautifully preserved, among which are many different species of oaks, beeches, poplars, plane-trees, vines, walnuts, plums, chestnuts, sequoias, and numerous shrubs--137 species in all, indicating a vegetation such as now grows in the north temperate parts of America and Eastern Asia. And even further north, in Spitzbergen, in N. lat. 78° and 79°, a somewhat similar flora is found, not quite so varied, but with oaks, poplars, birches, planes, limes, hazels, pines, and many aquatic plants such as may now be found in West Norway and in Alaska, nearly twenty degrees further south. Still more remote, in the Cretaceous period, fossil plants have been found in Greenland, consisting of ferns, cycads, conifers, and such trees and shrubs as poplars, sassafras, andromedas, magnolias, myrtles, and many others, similar in character and often identical in species with fossils of the same period found in Central Europe and the United States, indicating a widespread uniformity of climate, such as would be brought about by the great ocean-currents carrying the warm waters of the tropics into the Arctic seas.