CHAPTER 1. XIII. — THE WRITING OF THE 'ORIGIN OF SPECIES.'

little doubt; the land, on a LARGE SCALE, held much its present disposition: the species were mainly, judging from shells, what they are now. At this period when all animals and plants ranged 10 or 15 degrees nearer the poles, I believe the northern part of Siberia and of North America being almost CONTINUOUS, were peopled (it is quite possible, considering the shallow water, that Behring Straits were united, perhaps a little southward) by a nearly uniform fauna and flora, just as the Arctic regions now are. The climate then became gradually colder till it became what it now is; and then the temperate parts of Europe and America would be separated, as far as migration is concerned, just as they now are. Then came on the Glacial period, driving far south all living things; middle or even southern Europe being peopled with Arctic productions; as the warmth returned, the Arctic productions slowly crawled up the mountains as they became denuded of snow; and we now see on their summits the remnants of a once continuous flora and fauna. This is E. Forbes' theory, which, however, I may add, I had written out four years before he published.