[215] For La Plata, see my ‘Journal of Researches,’ during the voyage of the Beagle, 1845, p. 133. Élie de Beaumont has given (‘Leçons de Géolog. pratique,’ tom. I. 1845, p. 183) an excellent account of the enormous quantity of dust which is transported in some countries. I cannot but think that Mr. Proctor has somewhat exaggerated (‘Pleasant Ways in Science,’ 1879, p. 379) the agency of dust in a humid country like Great Britain. James Geikie has given (‘Prehistoric Europe,’ 1880, p. 165) a full abstract of Richthofen’s views, which, however, he disputes.
[217a] These statements are taken from Hensen in ‘Zeitschrift für wissenschaft. Zoologie.’ Bd. xxviii., 1877, p. 360. Those with respect to peat are taken from Mr. A. A. Julien in ‘Proc. American Assoc. Science,’ 1879, p. 354.
[217b] I have given some facts on the climate necessary or favourable for the formation of peat, in my ‘Journal of Researches,’ 1845, p. 287.
[220] A. A. Julien “On the Geological action of the Humus-acids,” ‘Proc. American Assoc. Science,’ vol. xxviii., 1879, p. 311. Also on “Chemical erosion on Mountain Summits;” ‘New York Academy of Sciences,’ Oct. 14, 1878, as quoted in the ‘American Naturalist.’ See also, on this subject, S. W. Johnson, ‘How Crops Feed,’ 1870, p. 138.
[222] See, for references on this subject, S. W. Johnson, ‘How Crops Feed,’ 1870, p. 326.
[223] This statement is taken from Mr. Julien, ‘Proc. American Assoc. Science,’ vol. xxviii., 1879, p. 330.
[224a] The preservative power of a layer of mould and turf is often shown by the perfect state of the glacial scratches on rocks when first uncovered. Mr. J. Geikie maintains, in his last very interesting work (‘Prehistoric Europe,’ 1881), that the more perfect scratches are probably due to the last access of cold and increase of ice, during the long-continued, intermittent glacial period.
[224b] Many geologists have felt much surprise at the complete disappearance of flints over wide and nearly level areas, from which the chalk has been removed by subaerial denudation. But the surface of every flint is coated by an opaque modified layer, which will just yield to a steel point, whilst the freshly fractured, translucent surface will not thus yield. The removal by atmospheric agencies of the outer modified surfaces of freely exposed flints, though no doubt excessively slow, together with the modification travelling inwards, will, as may be suspected, ultimately lead to their complete disintegration, notwithstanding that they appear to be so extremely durable.
[225a] ‘Archives de Zoolog. expér.’ tom. iii. 1874, p. 409.
[225b] ‘Nouvelles Archives du Muséum,’ tom. viii. 1872, pp. 95, 131.