Part 49 (1/2)

No similarly intercalated layer of marine sh.e.l.ls has been noticed in the neighbouring coal-field of Newcastle, where, as in South Wales and Somersets.h.i.+re, the marine deposits are entirely below those containing terrestrial and freshwater remains.[326-A]

_Clay-iron-stone._--Bands and nodules of clay-iron-stone are common in coal-measures, and are formed, says Sir H. De la Beche, of carbonate of iron, mingled mechanically with earthy matter, like that const.i.tuting the shales. Mr. Hunt, of the Museum of Practical Geology, inst.i.tuted a series of experiments to ill.u.s.trate the production of this substance, and found that decomposing vegetable matter, such as would be distributed through all coal strata, prevented the farther oxidation of the proto-salts of iron, and converted the peroxide into protoxide by taking a portion of its oxygen to form carbonic acid. Such carbonic acid, meeting with the protoxide of iron in solution, would unite with it and form a carbonate of iron; and this mingling with fine mud, when the excess of carbonic acid was removed, might form beds or nodules of argillaceous iron-stone.[326-B]

FOOTNOTES:

[308-A] Phillips; art. ”Geology,” Encyc. Britan.

[309-A] Sedgwick, Geol. Trans., Second Series, vol. iv.; and Phillips, Geol. of Yorksh. part 2.

[309-B] Memoirs of Geol. Survey, vol. i. p. 195.

[315-A] The trunk in this case is referred by Mr. Brown to _Lepidodendron_, but his ill.u.s.trations seem to show the usual markings a.s.sumed by _Sigillaria_ near its base.

[316-A] For terminology of cla.s.sification of plants, see above, note, p. 223.

[316-B] Quart. Geol. Journ., vol. v., Mem., p. 17.

[317-A] Anniv. Address to Geol. Soc., 1840.

[317-B] Hawkshaw, Geol. Soc. Proceedings, Nos. 64. and 69.

[318-A] Geol. Report on Cornwall, &c. p. 143.

[318-B] Lindley and Hutton, Foss. Flo. part 6. p. 150.

[319-A] See papers by Messrs. Beckett and Ick. Proceed. in Geol. Soc., vol. iv. p. 287.

[319-B] Annales des Mines, 1821.

[320-A] Principles of Geol., 8th ed., p. 215.

[321-A] See figures of texture, Witham, Foss. Veget., pl. 3.

[321-B] See Lyell's Travels in N. America, vol. ii. p. 179.

[322-A] Quart. Geol. Journ., vol. ii. p. 177.

[324-A] Geol. Quart. Journ., vol. ii. p. 393.; and vol. vi. p. 115.

[325-A] Prestwich, Geol. Trans., 2d Series, vol. v. p. 440. Murchison, Silurian System, p. 105.

[325-B] Silurian System, p. 84.

[325-C] Trans. Roy. Soc. Edin. vol. xiii. Horner, Edin. New Phil.

Journ., April, 1836.

[325-D] Phillips; art. ”Geology,” Encyc. Metrop., p. 590.

[326-A] Phillips; art. ”Geology,” Encyc. Metrop., p. 592.

[326-B] Memoirs of Geol. Survey, pp. 51. 255, &c.

CHAPTER XXV.

CARBONIFEROUS GROUP--_continued_.