Part 52 (2/2)

[Ill.u.s.tration: Fig. 404. _Strygocephalus Burtini_. (_Terebratula porrecta_, Sow.) Eifel; also South Devon.

_a._ valves united.

_b_. side view of same.

_c._ interior of larger valve, showing thick part.i.tion, and thinner one continued from it.]

[Ill.u.s.tration: Fig. 405. _Megalodon cucullatus_, Sow. Eifel; also Bradley, S. Devon.

_a._ the valves united.

_b._ interior of valve, showing the large cardinal tooth.]

[Ill.u.s.tration: Fig. 406. _Clymenia linearis_, Munster. (_Endosiphonites carinatus_, Ansted.) Cornwall.]

A peculiar species of trilobite, called _Brontes flabellifer_ (fig. 407.), is found in the Devonian strata of the Eifel and in South Devon. It should be observed, however, that the head in the specimen here figured by Goldfuss, the most perfect which could be obtained, is incomplete, and a restoration has been attempted by Mr. Salter in fig. 408., from data supplied by other species of the same genus occurring in older rocks.

[Ill.u.s.tration: Fig. 407. _Brontes flabellifer_, Goldf. Eifel; also S. Devon.]

[Ill.u.s.tration: Fig. 408. Restored outline of head of _Brontes flabellifer_.]

For determining the true equivalents of the Devonian group in the Rhenish provinces and adjacent parts of Germany, we are indebted to the labours of Messrs. Sedgwick and Murchison, in 1839, from which it appears that rocks of that age emerge from beneath the coal-field of Westphalia, and are also found in troughs among the Silurian rocks in Na.s.sau. Many of the limestones, particularly those on the river Lahn, are identical, both in structure and in coralline remains, with the beautiful marbles of Babbacombe, Torquay, and Plymouth.

The limestones of the Eifel, long ago celebrated for their fossils, and which lie in a basin supported by Silurian rocks, are found to be referable to the lower part of the Devonian system.

In Russia, also, Messrs. Murchison and De Verneuil have shown (1840) that the ”Old Red” group occupies a wide area south from St. Petersburg. It was formerly supposed to be the New Red Sandstone, on account of its saliferous and gypseous beds; but it is now proved to be the Old Red by containing ichthyolites of genera which characterize this group in the British Isles, as, for example, _Holoptychius_, _Coccosteus_, _Diplopterus_, &c.[349-A], a.s.sociated with mollusca found in the Devonian of Western Europe. Among the fish are also many species of sharks of the Cestraciont division, a fact worthy of notice, because the squaloid fishes of the present day offer the highest organization of the brain and of the generative organs, and make, in these respects, the nearest approach to the higher vertebrate cla.s.ses.

_Devonian Strata in the United States._

The position of this formation between the carboniferous rocks of Pennsylvania and Ohio, is pointed out in the section, fig. 379. p. 327., and it is a remark of M. de Verneuil that in no European country is there so complete and uninterrupted a development of the Devonian system as in North America. At the falls of the Ohio, at Louisville, in Kentucky, there is a grand display of one of the limestones of this period, resembling a modern coral reef. A wide extent of surface is exposed in a series of horizontal ledges, at all seasons, when the water is not high; and the softer parts of the stone having decomposed and wasted away, the harder calcareous corals stand out in relief, and many of them send out branches from their erect stems precisely as if they were living. Among other species I observed large ma.s.ses, not less than 5 feet in diameter, of _Favosites gothlandica_, with its beautiful honeycomb structure well displayed, and, by the side of it, the _Favistella_, combining a similar honeycombed form with the star of the _Astrea_. There was also the cup-shaped _Cyathophyllum_, and the delicate network of the _Fenestella_, and that elegant and well-known European species of fossil, called ”the chain coral,” _Catenipora escharoides_, with a profusion of others (see fig. 423. p. 355.). These coralline forms were mingled with the joints, stems, and occasionally the heads, of lily encrinites. Although hundreds of fine specimens have been detached from these rocks, to enrich the museums of Europe and America, another crop is constantly working its way out, under the action of the stream, and of the sun and rain, in the warm season when the channel is laid dry. The waters of the Ohio, when I visited the spot in April, 1846, were more than 40 feet below their highest level, and 20 feet above their lowest, so that large s.p.a.ces of bare rock were exposed to view.[349-B]

_Devonian Flora._

With the exception of the fucoids above mentioned (p. 344.), but little is known with certainty of the plants of the Devonian group. Those found in the department of La Sarthe in France, and in various parts of Brittany, formerly referred to the Devonian era, have been shown (in 1850), by M. de Verneuil, to belong to the carboniferous series. The same may be said of the species of _Lepidodendron_, _Knorria_, _Calamite_, _Sagenaria_, and other genera recently figured (1850), by Mr. F. A. Romer, from the formation called ”Greywacke a Posodonomyes” in the Hartz.[350-A] They are accompanied by _Goniat.i.tes reticulatus_ Phillips, _G. intercostatus_ Phil., and other mountain limestone species, and had been previously a.s.signed to the oldest part of the carboniferous series by Messrs. Murchison and Sedgwick.

If hereafter we should become well acquainted with the land plants of the Devonian era, we may confidently expect that nearly all of them will agree generically with those of the carboniferous period, but the species will be as different as are the Devonian vertebrate and invertebrate animals from the fossil species of the Coal.

FOOTNOTES:

[342-C] See section, fig. 318. p. 287.

[343-A] The Old Red Sandstone, by Hugh Miller, 1841.

[345-A] Old Red Sandstone. Plate 1. fig. 1. Mr. M.'s description of the fish is most graphic and correct.

[347-A] Camb. Phil. Trans., vol. vi. pl. 8. fig. 2.

[349-A] See Proceedings of Geol. Soc., and the anniversary speech of Dr. Buckland, P. G. S., for 1841.

[349-B] Lyell's Second Visit to the United States, vol. ii. p. 277.

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