[167] Compare Squier's Central America, vol. i. pp. 34, 244, 358, 421, vol. ii. p. 307, with Journal of Geograph. Society, vol. iii. p. 59, vol. viii. pp. 319, 323.
[168] Mr. Squier (Central America, vol. ii. p. 68); who explored Nicaragua, says of the statues, ‘the material, in every case, is a black basalt, of great hardness, which, with the best of modern tools, can only be cut with difficulty.’ Mr. Stephens (Central America, vol. ii. p. 355) found at Palenque ‘elegant specimens of art and models for study.’ See also vol. iii. pp. 276, 389, 406, vol. iv. p. 293. Of the paintings at Chichen he says (vol. iv. p. 311), ‘they exhibit a freedom of touch which could only be the result of discipline and training under masters.’ At Copan (vol. i. p. 151), ‘it would be impossible, with the best instruments of modern times, to cut stones more perfectly.’ And at Uxmal (vol. ii. p. 431), ‘throughout, the laying and polishing of the stones are as perfect as under the rules of the best modern masonry.’ Our knowledge of Central America is almost entirely derived from these two writers; and although the work of Mr. Stephens is much the more minute, Mr. Squier says (vol. ii. p. 306), what I believe is quite true, that until the appearance of his own book in 1853, the monuments in Nicaragua were entirely unknown. Short descriptions of the remains in Guatemala and Yucatan will be found in Larenaudière's Mexique et Guatemala, pp. 308–327, and in Journal of Geograph. Society, vol. iii. pp. 60–63.
[169] See the remarks on Yucatan in Prichard's Physical History of Mankind, vol. v. p. 348: ‘a great and industrious, though perhaps, as the writer above cited (Gallatin) observes, an enslaved population. Splendid temples and palaces attest the power of the priests and nobles, while as usual no trace remains of the huts in which dwelt the mass of the nation.’
[170] Dr. M'Culloh (Researches concerning the Aboriginal History of America, pp. 272–340) has collected from the Spanish writers some meagre statements respecting the early condition of Central America; but of its social state and history, properly so called, nothing is known; nor is it even certain to what family of nations the inhabitants belonged, though a recent author can find ‘la civilisation guatemalienne ou misteco-zapotèque et mayaquiche vivante pour nous encore dans les ruines de Mitla et de Palenque.’ Mexique et Guatemala, par Larenaudière, p. 8, Paris, 1843. Dr. Prichard, too, refers the ruins in Central America to ‘the Mayan race:’ see Prichard on Ethnology, in Report of British Association for 1847, p. 252. But the evidence for these and similar statements is very unsatisfactory.
[171] Respecting the connection between the vegetable productions of a country and its geognostic peculiarities, little is yet known; but the reader may compare Meyen's Geography of Plants, p. 64, with Reports on Botany by the Ray Society, 1846, pp. 70, 71. The chemical laws of soil are much better understood, and have a direct practical bearing on the use of manures. See Turner's Chemistry, vol. ii. pp. 1310–1314; Brande's Chemistry, vol. i. p. 691, vol. ii. pp. 1867–1869; Balfour's Botany, pp. 116–122; Liebig and Kopp's Reports, vol. ii. pp. 315, 328, vol. iii. p. 463, vol. iv. pp. 438, 442, 446.
[172] As to the influence of heat and moisture on the geographical distribution of plants, see Henslow's Botany, pp. 295–300, and Balfour's Botany, pp. 560–563. Meyen (Geog. of Plants, p. 263) says, ‘I, therefore, after allowing for local circumstances, bring the vegetation of islands also under the law of nature, according to which the number of species constantly increases with increasing heat and corresponding humidity.’ On the effect of temperature alone, compare a note in Erman's Siberia, vol. i. pp. 64, 65, with Reports on Botany by the Ray Society, pp. 339, 340. In the latter work, it is supposed that heat is the most important of all single agents; and though this is probably true, still the influence of humidity is immense. I may mention as an instance of this, that it has been recently ascertained that the oxygen used by seeds during germination, is not always taken from the air, but is obtained by decomposing water. See the curious experiments of Edwards and Colin in Lindley's Botany, vol. ii. pp. 261, 262, London, 1848; and on the direct nourishment which water supplies to vegetables, see Burdache's great work, Traité de Physiologie, vol. ix. pp. 254, 398.
[173] There is a difference between the watersheds of the eastern and western ranges, which explains this in part, but not entirely; and even if the explanation were more satisfactory than it is, it is too proximate to the phenomenon to have much scientific value, and must itself be referred to higher geological considerations.
[174] Of this irrigation some idea may be formed from an estimate that the Amazon drains an area of 2,500,000 square miles; that its mouth is 96 miles wide; and that it is navigable 2,200 miles from its mouth. Somerville's Physical Geography, vol. i. p. 423. Indeed, it is said in an essay on the Hydrography of South America (Journal of Geograph. Society, vol. ii. p. 250), that ‘with the exception of one short portage of three miles, water flows, and is for the most part navigable, between Buenos Ayres, in 35° south latitude, to the mouth of the Orinoco, in nearly 9° north.’ See also on this river-system, vol. v. p. 93, vol. x. p. 267. In regard to North America, Mr. Rogers (Geology of North America, p. 8, Brit. Assoc. for 1834) says, ‘the area drained by the Mississippi and all its tributaries is computed at 1,099,000 square miles.’ Compare Richardson's Arctic Expedition, vol. ii. p. 164.
[175] The Oregon, or Columbia as it is sometimes called, forms a remarkable botanical line, which is the boundary of the Californian flora. See Reports on Botany by the Ray Society, p. 113.
[176] For proof that the mean temperature of the western coast of North America is higher than that of the eastern coast, see Journal of Geograph. Society, vol. ix. p. 380, vol. xi. pp. 168, 216; Humboldt, la Nouvelle Espagne, vol. i. pp. 42, 336; Richardson's Arctic Expedition, vol. ii. pp. 214, 218, 219, 259, 260. This is well illustrated by the botanical fact, that on the west coast the Coniferæ grow as high as 68° or 70° north latitude; while on the east their northern limit is 60°. See an Essay on the Morphology of the Coniferæ, in Reports on Botany by the Ray Society, p. 8, which should be compared with Forry on the Climate of the United States and its Endemic Influences, New York, 1842, p. 89.