A Manual of Elementary Geology Part 43

[276-C] Ibid. p. 168.

[276-D] Ibid. p. 187.

[277-A] Geol. Soc. Proceedings, vol. iii. p. 157. 1839.

[277-B] Geol. Trans. Second Series, vol. v. p. 511.

[278-A] Geol. Trans., Second Series, vol. i. pl. 49.

[278-B] Conybeare and De la Beche. Geol. Trans.; and Buckland, Bridgew. Treat., p. 203.

[278-C] Quart. Geol. Journ. vol. ii. p. 411.

[279-A] +Amblys+, _amblys_, blunt; and +rhygchos+, _rhynchus_, snout.

[280-A] Darwin's Journal, chap. xix.

[280-B] Bridgew. Treat., p. 125.

[281-A] Geological Researches, p. 334.

[281-B] Buckland, Bridgew. Treat., p. 307.

[281-C] Ibid.

[281-D] See Principles, _Index_, Lancerote, Graham Island, Calabria.

[281-E] A History of Fossil Insects, &c. 1845. London.

[282-A] Tableau des Veg. Fos. 1849, p. 105.

[283-A] Con. and Phil., p. 166.

[283-B] Geol. Researches, p. 337.

[283-C] Burat's D'Aubuisson, tom. ii. p. 456.

[285-A] See description of the coal-field by the author, and the plants by C. J. F. Bunbury, Esq., Quart. Geol. Journ., vol. iii. p. 281.

CHAPTER XXII.

TRIAS OR NEW RED SANDSTONE GROUP.

Distinction between New and Old Red Sandstone--Between Upper and Lower New Red--The Trias and its three divisions--Most largely developed in Germany--Keuper and its fossils--Muschelkalk--Fossil plants of Bunter--Tria.s.sic group in England--Bone-bed of Axmouth and Aust--Red Sandstone of Warwickshire and Cheshire--Footsteps of _Chirotherium_ in England and Germany--Osteology of the _Labyrinthodon_--Identification of this Batrachian with the Chirotherium--Origin of Red Sandstone and Rock-salt--Hypothesis of saline volcanic exhalations--Theory of the precipitation of salt from inland lakes or lagoons--Saltness of the Red Sea--New Red Sandstone in the United States--Fossil footprints of birds and reptiles in the Valley of the Connecticut--Antiquity of the Red Sandstone containing them.

Between the Lias and the Coal, or Carboniferous group, there is interposed, in the midland and western counties of England, a great series of red loams, shales, and sandstones, to which the name of the New Red Sandstone formation was first given, to distinguish it from other shales and sandstones called the "Old Red" (_c_, fig. 318.), often identical in mineral character, which lie immediately beneath the coal (_b_).

[Ill.u.s.tration: Fig. 318. Cross section.

_a._ New red sandstone.

_b._ Coal.

_c._ Old red.]

The name of "Red Marl" has been incorrectly applied to the red clays of this formation, as before explained (p. 13.), for they are remarkably free from calcareous matter. The absence, indeed, of carbonate of lime, as well as the scarcity of organic remains, together with the bright red colour of most of the rocks of this group, causes a strong contrast between it and the Jura.s.sic formations before described.

Before the distinctness of the fossil remains characterizing the upper and lower part of the English New Red had been clearly recognized, it was found convenient to have a common name for all the strata intermediate in position between the Lias and Coal; and the term "Poikilitic" was proposed by Messrs. Conybeare and Buckland[286-A], from +poikilos+, poikilos, _variegated_, some of the most characteristic strata of this group having been called _variegated_ by Werner, from their exhibiting spots and streaks of light-blue, green, and buff colour, in a red base.

A single term, thus comprehending both Upper and Lower New Red, or the Tria.s.sic and Permian groups of modern cla.s.sifications, may still be useful in describing districts where we have to speak of ma.s.ses of red sandstone and shale, referable, in part, to both these eras, but which, in the absence of fossils, it is impossible to divide.

_Trias or Upper New Red Sandstone Group._

The accompanying table will explain the subdivisions generally adopted for the uppermost of the two systems above alluded to, and the names given to them in England and on the Continent.

Synonyms.

German. French.

{ _a._ Saliferous and } } { gypseous shales and } Keuper } Marnes irisees.

Trias or Upper { sandstone } } New Red { Sandstone { _b._ (wanting in England) } Muschelkalk { Muschelkalk, ou { { calcaire { { coquillier.

{ { _c._ Sandstone and } Bunter- } Gres bigarre.

{ quartzose conglomerate } sandstein }

I shall first describe this group as it occurs in South Western and North Western Germany, for it is far more fully developed there than in England or France. It has been called the Trias by German writers, or the Triple Group, because it is separable into three distinct formations, called the "Keuper," the "Muschelkalk," and the "Bunter-sandstein."

[Ill.u.s.tration: Fig. 319. _Equiset.i.tes columnaris._ (Syn. _Equisetum columnare_.) Fragment of stem, and small portion of same magnified. Keuper.]

_The Keuper_, the first or newest of these, is 1000 feet thick in Wurtemberg, and is divided by Alberti into sandstone, gypsum, and carbonaceous slate-clay.[287-A] Remains of Reptiles, called _Nothosaurus_ and _Phytosaurus_, have been found in it with _Labyrinthodon_; the detached teeth, also, of placoid fish and of rays, and of the genera _Saurichthys_ and _Gyrolepis_ (figs. 325, 326, p. 289.). The plants of the Keuper are generically very a.n.a.logous to those of the lias and oolite, consisting of ferns, equisetaceous plants, cycads, and conifers, with a few doubtful monocotyledons. A few species, such as _Equiset.i.tes columnaris_, are common to this group, and the oolite.

_The Muschelkalk_ consists chiefly of a compact, greyish limestone, but includes beds of dolomite in many places, together with gypsum and rock-salt. This limestone, a rock wholly unrepresented in England, abounds in fossil sh.e.l.ls, as the name implies. Among the cephalopoda there are no belemnites, and no ammonites with foliated sutures, as in the inc.u.mbent lias and oolite, but a genus allied to the Ammonite, called _Cerat.i.te_ by De Haan, in which the descending lobes (see _a_, _b_, _c_, fig. 320.) terminate in a few small denticulations pointing inwards. Among the bivalve sh.e.l.ls, the _Posidonia minuta_, Goldf. (_Posidonomya minuta_, Bronn) (see fig. 321.), is abundant, ranging through the Keuper, Muschelkalk, and Bunter-sandstein; and _Avicula socialis_, fig. 322., having a similar range, is very characteristic of the Muschelkalk in Germany, France, and Poland.

[Ill.u.s.tration: Fig. 320. _Cerat.i.tes nodosus._ Muschelkalk.

_a._ Side view.

_b._ Front view.

_c._ Partially denticulated outline of the septa dividing the chambers.]

[Ill.u.s.tration: Fig. 321. _Posidonia minuta_, Goldf. (_Posidonomya minuta_, Bronn.)]

[Ill.u.s.tration: Fig. 322. Avicula. Characteristic of the Muschelkalk.

_a._ _Avicula socialis._ _b._ Side view of same.]

The abundance of the heads and stems of lily encrinites, _Encrinus liliiformis_ (or _Encrinites moniliformis_), show the slow manner in which some beds of this limestone have been formed in clear sea-water.