On the whole, it may be concluded that had the Gulf-stream not returned to our shores at the close of the glacial epoch, and had its place been supplied by a cold stream from the polar regions, similar to that which washes the shores of North America, it is highly probable that nearly every species found in our glacial beds would have had their representatives flourishing in the British seas at the present day. It is no doubt true that when we compare the places in which the Canadian shell-beds referred to by Mr. Crosskey are situated with places on the same latitude in Europe, the difference of climate resulting from the influence of the Gulf-stream is not so great as between Scotland and those places which we have been considering; but still the difference is sufficiently great to account for why the change of climate in Canada has been less complete than in Scotland. And what holds true in regard to the currents of the Atlantic holds also true, though perhaps not to the same extent, of the currents of the Pacific. _Nearness of the Sun in Perigee a Cause of the Accumulation of Ice._—But there is still another cause which must be noticed:—A strong under current of air _from_ the north implies an equally strong upper current _to_ the north. Now if the effect of the under current would be to impel the warm water at the equator to the south, the effect of the upper current would be to carry the aqueous vapour formed at the equator to the north; the upper current, on reaching the snow and ice of temperate regions, would deposit its moisture in the form of snow; so that, notwithstanding the great cold of the glacial epoch, it is probable that the quantity of snow falling in the northern regions would be enormous. This would be particularly the case during summer, when the earth would be in the perihelion and the heat at the equator great. The equator would be the furnace where evaporation would take place, and the snow and ice of temperate regions would act as a condenser. Heat to produce _evaporation_ is just as essential to the accumulation of snow and ice as cold to produce _condensation_. Now at Midsummer, on the supposition of the eccentricity being at its superior limit, the sun would be 8,641,870 miles nearer than at present during that season. The effect would be that the intensity of the sun’s rays would be one-fifth greater than now. That is to say, for every five rays received by the ocean at present, six rays would be received then, consequently the evaporation during summer would be excessive. But the ice-covered land would condense the vapour into snow. It would, no doubt, be during summer that the greatest snowfall would take place. In fact, the nearness of the sun during that season was as essential to the production of the glacial epoch as was his distance during winter.