Principles of Geology Part 73

[135] Rafinesque, Atlantic Journ., p. 18.

[136] Darwin's Journal of Travels in South America, &c., 1832 to 1836, in Voyage of H. M. S. Beagle, p. 159.

[137] Ehrenberg, ibid.

[138] The speculations which follow, on the ancient physical geography of Siberia, and its former fitness as a residence for the mammoth, were first given in their present form in my 4th edition, June, 1835. Recently Sir R. Murchison and his companions in their great work on the Geology of Russia, 1845 (vol. i. p. 497), have, in citing this chapter, declared that their investigations have led them to similar conclusions.

Professor Owen, in his excellent History of British Fossil Mammalia, 1844, p. 261, _et seq._, observes that the teeth of the mammoth differ from those of the living Asiatic or African elephant in having a larger proportion of dense enamel, which may have enabled it to subsist on the coa.r.s.er ligneous tissues of trees and shrubs. In short, he is of opinion, that the structure of its teeth, as well as the nature of its epidermis and coverings, may have made it "a meet companion for the reindeer."

[139] Pallas, Reise in Russ. Reiche, pp. 409, 410.

[140] Nov. Com. Petrop. vol. xvii. p. 584.

[141] Nov. Com. Petrop. vol. xvii. p. 591.

[142] Quart. Journ. Geol. Soc. Lond. vol. iv. p. 10, Memoirs.

[143] Journal du Nord, St. Petersburg, 1807.

[144] Fleming, Ed. New Phil. Journ., No. xii. p. 285.

Bishop Heber informs us (Narr. of a Journey through the Upper Provinces of India, vol. ii. p. 166-219), that in the lower range of the Himalaya mountains, in the northeastern borders of the Delhi territory, between lat. 29 and 30, he saw an Indian elephant of a small size, covered with s.h.a.ggy hair. But this variety must be exceedingly rare; for Mr. Royle (late superintendent of the East India Company's Botanic Garden at Saharunpore) has a.s.sured me, that being in India when Heber's Journal appeared, and having never seen or heard of such elephants, he made the strictest inquiries respecting the fact, and was never able to obtain any evidence in corroboration. Mr.

Royle resided at Saharunpore, lat. 30 N., upon _the extreme northern limits_ of the range of the elephant. Mr. Everest also declares that he has been equally unsuccessful in finding any one aware of the existence of such a variety or breed of the animal, though one solitary individual was mentioned to him as having been seen at Delhi, with a good deal of long hair upon it. The greatest elevation, says Mr. E., at which the wild elephant is found in the mountains to the north of Bengal, is at a place called Nahun, about 4000 feet above the level of the sea, and in the 31st degree of N. lat., where the mean yearly temperature may be about 64 Fahrenheit, and the difference between winter and summer very great, equal to about 36 F., the month of January averaging 45, and June, the hottest month, 81 F. (Everest on climate of Foss. Eleph., Journ. of Asiat. Soc., No. 25, p. 21.)

[145] See Dr. Buckland's description of these bones, Appen. to Beechy's Voy.

[146] Darwin, Journal of Travels in S. America, &c., 1832-36, in voyage of H. M. S. Beagle, p. 98. 2d Ed. London, 1845, p.

86.

[147] Darwin, Journal of Travels in S. America, &c., p. 99, 2d Ed. p. 85.

[148] Burch.e.l.l, cited by Darwin, ibid. p. 101. 2d Ed. p. 87.

[149] Since the above pa.s.sage was first printed in a former edition, June, 1835, it has been shown by the observations of Sir R. Murchison, M. de Verneuil, and Count Keyserling, and more recently by M. Middendorf (see above, p. 81), that the Lowland of Siberia has actually been extended, since the existing species of sh.e.l.ls inhabited the northern seas.

[150] Humboldt, Fragmens Asiatiques, tom. ii. p. 393.

[151] Reboul. Geol. de la Periode Quaternaire, who cites Observ. sur la Siberie, Bibl. Univ., Juillet, 1832.

[152] Conjectured to be the wild stock of Bos grunniens.

[153] Recollections of a Journey through Tartary, Thibet, and China (ch. xv. p. 234), by M. Huc. Longman, 1852.

[154] For an account of the more modern changes of the tertiary fauna and flora of the British Isles and adjoining countries, and particularly those facts which relate to the "glacial epoch," see an admirable essay by Prof. E. Forbes. Memoirs of Geol. Survey of Great Brit. vol. i. p. 336. London, 1846. To this important memoir I shall have frequent occasion to refer in the sequel.

[155] See a paper by Charles J. F. Bunbury, Esq., Journ. of Geol. Soc., London, No. 6, p. 88. 1846.

[156] The Calamites were formerly regarded by Adolphe Brongniart as belonging to the tribe of Equisetaceae; but he is now inclined to refer them to the cla.s.s of gymnogens, or gymnospermous exogens, which includes the Coniferae and Cycadeae.

Lepidodendron appears to have been either a gigantic form of the lycopodium tribe, or, as Dr. Lindley thinks, intermediate between the lycopodia and the fir tribe. The Sigillariae were formerly supposed by Ad. Brongniart, to be arborescent ferns; but the discovery of their internal structure, and of their leaves, has since proved that they have no real affinity to ferns. According to the view now taken of their structure, their nearest allies in the recent world are the genera Cycas and Zamia; while Corda, on the other hand, maintains that they were closely related to the succulent euphorbias. Stigmaria is now generally admitted to have been merely the root of sigillaria. The scalariform vessels of these two genera are not conclusive in proving them to have a real affinity with ferns, as Mr. Brown has discovered the same structure of vessels in Myzodendron, a genus allied to the mistletoe; and Corda has lately shown that in two species of Stigmaria, hardly distinguishable by external characters, the vessels of the one are scalariform, and of the other dotted.

[157] Mr. Lindley endeavored formerly (1834) to show, in the "Fossil Flora," that Trigonocarpum Noeggerathii, a fruit found in the coal measures, has the true structure of a palm-fruit; but Ad. Brongniart has since inclined to regard it as cycadeous; nor is the French botanist satisfied that some specimens of supposed palm wood from the coal-mines of Radnitz in Bohemia, described by Corda, really belong to palms. On the other hand, Corda has proved Flabellaria bora.s.sifolia of Sternberg to be an exogenous plant, and Brongniart contends that it was allied to the Cycadeae. See Tableau des Genres de Vegetaux Fossiles. Paris, 1849.

[158] Prodrome d'une Hist. des Veget. Foss. p. 179. See also a late paper, Quart. Journ. of Geol. Soc. London, 1846, in which coal-plants of Alabama, lat. 33 N., collected by the author, are identified by Mr. Bunbury with British fossil species, showing the great southern extension of this flora.

[159] Konig, Journ. of Sci., vol. xv. p. 20. Mr. Konig informs me that he no longer believes any of these fossils to be tree ferns, as he at first stated, but that they agree generically with plants in our English coal-beds. The Melville Island specimens, now in the British Museum, are very obscure impressions.

[160] Fossil Flora of Great Britain, by John Lindley and William Hutton, Esqrs., No. IV.

[161] Fossil Flora of Great Britain, by John Lindley and William Hutton, Esqrs. No. IV.

[162] Fossil Flora, No. X.

[163] This has been proved by Mr. Lindley's experiments, ibid.

No. XVII.

[164] I have treated of this subject in my Manual of Geology, and still more fully in my Travels in N. America, vol. ii. p.

178. For a full account of the facts at present known, and the theories entertained by the most eminent geologists and botanists on this subject, see Mr. Horner's Anniversary Address to the Geological Society of London, February, 1846. Consult also Sir H. de la Beche, on the formation of rocks in South Wales, Memoirs of Geol. Survey of Great Britain, 1846, p. 1 to 296.

[165] The theory proposed in this and the following chapters, to account for former fluctuations of climate at successive geological periods, agrees in every essential particular, and has indeed been reprinted almost verbatim from that published by me twenty years ago in the first edition of my Principles, 1830. It was referred to by Sir John F. W. Herschel in his Discourse on Natural Philosophy, published in 1830. In preceding works the gradual diminution of the earth's central heat was almost the only cause a.s.signed for the acknowledged diminution of the superficial temperature of our planet.

[166] We are indebted to Baron Alex. von Humboldt for having first collected together the scattered data on which he founded an approximation to a true theory of the distribution of heat over the globe. Many of these data were derived from the author's own observations, and many from the works of M. Pierre Prevost, of Genera, on the radiation of heat, and from other writers.--See Humboldt on Isothermal Lines, Memoires d'Arcueil, tom. iii. translated in the Edin. Phil. Journ. vol. iii. July, 1820.

The map of Isothermal Lines, recently published by Humboldt and Dove (1848), supplies a large body of well-established data for such investigations, of which Mr. Hopkins has most ably availed himself in an essay "On the Causes which may have produced Changes in the earth's Superficial Temperature."--Q. Journ.

Geol. Soc. 1852, p. 56.

[167] Sir J. Richardson's Appendix to Sir G. Bach's Journal, 1843-1845, p. 478.

[168] Malte-Brun, Phys. Geol. book xvii.

[169] On Isothermal Lines, &c.

[170] Rennell on Currents, p. 96. London, 1832.

[171] Ibid. p. 153.

[172] Ibid. p. 25.

[173] Scoresby's Arctic Regions, vol. i. p. 208.--Dr. Latta's Observations on the Glaciers of Spitzbergen, &c. Edin. New Phil. Journ. vol. iii. p. 97.

[174] Rennell on Currents, p. 95.

[175] Humboldt on Isothermal Lines.

[176] Journ. of Travels in S. America, &c. p. 272.

[177] Darwin's travels in S. America, p. 271.

[178] Mr. Hopkins raises the question whether, in South Georgia, the descent of glaciers to the margin of the sea might not have been mistaken by Capt. Cook for the descent of the snow-line to the sea level. Quart. Journ. Geol. Soc. p. 85, 1852. The great navigator is generally very accurate, and there seem to be no observations of more recent date either to confirm or invalidate his statements.