[83]. Aug. Thierry, Histoire de la Conquête d’Angleterre, vol. i, p. 155.
[84]. Lyell, “Principles of Geology,” vol. i, p. 178.
[85]. Link, Die Urwelt und das Altertum, vol. i, p. 84.
[86]. Link, op. cit., vol. i, p. 91.
[87]. Cuvier, op. cit. Compare also, on this point, the opinion of Alexander von Humboldt: “In the epochs preceding the existence of the human race the action of the forces in the interior of the globe must, as the earth’s crust increased in thickness, have modified the temperature of the air and made the whole earth habitable by the products which we now regard as exclusively tropical. Afterwards the spatial relation of our planet to the central body (the sun) began, by means of radiation and cooling down, to be almost the sole agent in determining the climate at different latitudes. It was also in these primitive times that the elastic fluids, or volcanic forces, inside the earth, more powerful than they are to-day, made their way through the oxidized and imperfectly solidified crust of our planet” (Asie centrale, vol. i, p. 47).
[88]. Second edition, pp. 92–4. The man was born in 1727.
[89]. See Genesis ii, 8, 10, 15.
[90]. Lyell, “Principles of Geology,” vol. ii, p. 119.
[91]. Alexander von Humboldt does not think that this hypothesis can apply to the migration of plants. “What we know,” he says, “of the deleterious action exerted by sea-water, during a voyage of 500 or 600 leagues, over the reproductive power of most grains, does not favour the theory of the migration of vegetables by means of ocean currents. Such a theory is too general and comprehensive” (Examen critique de l’histoire de la géographie du nouveau continent, vol. ii, p. 78).
[92]. Alexander von Humboldt gives the law determining these facts in the following passage (Asie centrale, vol. iii, p. 23): “The foundation of the science of climatology is the accurate knowledge of the inequalities of a continent’s surface (hypsometry). Without this knowledge we are apt to attribute to elevation what is really the effect of other causes, acting, in low-lying regions, on a surface of which the curve is continuous with that of the sea, along the isothermic lines (i.e. lines along which the temperature is the same).” By calling attention to the multiplicity of influences acting on the temperature of any given geographical point, Von Humboldt shows how very different conditions of climate may exist in places that are quite near each other, independently of their height above sea-level. Thus in the north-east of Ireland, on the Glenarn coast, there is a region, on the same parallel of latitude as Königsberg in Prussia, which produces myrtles growing in the open air quite as vigorously as in Portugal; this region is in striking contrast with those round it. “There are hardly any frosts in winter, and the heat in summer is not enough to ripen the grapes.... The pools and small lakes of the Faroe Islands are not frozen over during the winter, in spite of the latitude (62°).... In England, on the Devonshire coast, the myrtle, the camelia iaponica, the fuchsia coccinea, and the Boddleya globosa flourish in the open, unsheltered, throughout the winter.... At Salcombe the winters are so mild that orange-trees have been seen, with fruit on them, sheltered by a wall and protected merely by screens” (pp. 147–48).