Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/367

Rh TaI1.ss1c.] coast of Devon»-hire, it contains casts of the cubical spaces once occupied by crystals of common salt. But in Cheshire the salt occurs in two or more beds, of which the lower is soiuetiines upwards of 100 feet thick. It is a crystalline substance, usually tinged yellow or red from intermixture of clay and peroxide of iron, but is tolerably pure in the best part of the beds, where the proportion of chloride of sodium is as much as 98 per cent. Through the bright red marls with which the salt is interstratiﬁed there run bands of gypsum, somewhat irregular in their mode of occurrence, sometimes reaching a thickness of 40 feet and upwards. Thin seams of rock-salt likewise occur among the red marls. These facts point to the concentration and evaporation of salt lakes or inland seas. The organic. remains of the Trias are comparatively few, as the conditions for at least animal life must have been extremely unfavourable in the waters of the ancient Dead Sea wherein these red rocks were aceiiniulatcd. The land possessed a vegetation which, from the few fragments yet known, seems to have consisted in large measure of K-_vpress-like coniferous ti'ees ( VoIt:z'('r, l!'uIchL'u), with calainites on the lower more marsliy grounds. The red marl group contains in some of its layers niiiueroiis valves of the little I.-rustacc-.in 1'.'stlzcr[u niinuta, and a solitary species of lamellibranch, .I’ul[u.s-tra m'cni'c0lu. A number of teeth, spines, and sometimes entire skclctins of fish have been obtained (Diptcronotus cyphus, 1’ulrconi'scus szq)crslrs, 113/borlus Kcu]zr'ri, Acrodus mz'm'm'us, rS'j)hcn0n- (‘hit-S‘ mi'ni'mus, Lnpliodus, &c.). The bones, and still more fre- -qnently the footprints, of labyrinthodont and even of saurian reptiles occur in the Kcupcr bcds—L(Ibyrinthoclon (4 species), Clmlgoilon L/oyclii, 1[_i/pcrudupcdon, Pulccosaurus, Temtosaurus, T]lCCOtl0}lt0S(tll)'lLS, 1Zli_i/ncosuurus, and footprints of Chci'r0tl¢c7'i'iml. The reniains of a small marsupial (jlicrolcstcs) have likewise been -diseo'ci'ed. 1’/uetic.—At the top of the Red Marl certain thin-bedded strata form a gradation upwards into the base of the Jurassic system. As their colours are grey and blue, and contrast with the red marls on which they repose conform- ably, they were formerly classed without hesitation in the Jurassic series. Egerton, however, showed that, from the character of their included ﬁsh remains, they had more palzeontological afﬁnity with the Trias than with the Lias. Subsequent research, particularly among the Rhaetic Alps and elsewhere on the Continent, brought to light a great series of strata of intermediate characters between the Trias and Lias. These results led to renewed examination of the so—called beds of passage in England, which were found to be truly representative of the massive formations of the T 'rolesa and Swiss Al The ' are therefore now classed 3 _ _ l 3 as Rhictic, and considered as the uppermost member of the Trias, but offering evidence of the gradual approach of the physical geography and characteristic fauna and ﬂora of the Jurassic period. The Rlnctic beds extend as a continuous though very thin band at the top of the Trias, from the coast of Yorkshire across England to Lyme Rcgis on the Dorscts_hire shores. They occur in scattered patches even up as far as C_arl1sle, and westwards on both sides of the Bristol Channel. Their thickness, on the avera e, is robabl , _ 8 P 3’ not more than 50 feet, though it rarely increases to 150 feet. They consist of thin-bedded grey and dark shales and clays, with bands of light-coloured limestone. One of their most important sub- divisions is the so—called Bone-bcd—a pyritous, micaeeous, and «occasionally rippled sandstone, sometimes in several bands, abound- ing in ﬁsh bones, teetli,coprolites, and other organic remains. The grey marly beds in the lower ‘iortion of the series have vielded remains of the Jlzcrolcstcs Rhrctzcus. Among the reptilian fossils are some precursors of the great forms which distinguished the Jurassic period (lchthyosaurus and Plcsiosaurus). The fishes include Acrodus -mim'mus, C'c-mtodus altus, II}/borlus minur, Nema- canthus moni'l{'7"cr, &e. Sonic of the laniellibranchs are specially characteristic; such are C'm'clium Rluvticitait, Aricula contorta, Pcctcn Vuloiticizsis, and Pullastra m'cm'coIa. Professor Ramsay has drawn attention to the probable geo- grapliieal changes recorded by the Triassic rocks of England. Con- necting them with the earlier and similar Permian sandstones and marls c points out that the great Continental period which began with the Old Red Sandstone closed with the New Red Marl, and was characterized by the existence of great lakes, many of which must have been salt, and by the abundance of labyrinthodont GEOLOGY 303 life. The Triassic rocks were, doubtless, laid down in one of these salt lakes round the margins of which the labyrintliodonts left their footprints on the soft sand. In the Rhzetie series we see how these inland basins were gradually invaded by the sea, which brought into the region of Britain the rich fauna of the Jurassic period. Cox'r1NE:'T_iL EUROPE.—-The Trias is the most compactly distributed of all the geological formations of Europe. Its main area extends as a great basin from Basel down to the plains of Hanover, traversed along its centre by the course of the Rhine, and stretching from the ﬂanks of the old high grounds of Saxony and Bohemia on the east across the Vosges mountains into France. This must have been a great inland sea, out of which the Harz mountains, and the high grounds of the Eifel, Huiidsruck, and Taunus probably rose as islands. It may have extended up to the base of the Alps, for enormous masses of Triassic rocks now form part of these mountains. Traces of what were probably other basins occur eastward in the Carpathian district, along the southern front of the Alps, in the west and south of France, and over the eastern half of the Spanish peninsula. But these areas have been considerably obscured, sometimes by dislocation and denudation, sometimes by the overlap of more recent formations. In the great German Triassic basin the deposits are as shown in the subjoined table. V Upper or Rh2ctie.—Grey sandy clays and ﬁne-grained sand- stones, containing Equz'sctum, Asplenitcs, and cycads (Zamitcs, Ptcropliyll um), sometimes forming thin seams of coal—C'ar- dium I-t’Iza"ticzmL, Aricula contorta, E.s'thcn'a mimtta, Nethe- sa-urus, Tcrmutosaur-us, Bcloclon, and Jlicrolcstcs antiquus. Middle (lluntc Kcnpcrmcrgcl, Gypskcupcr).——Bright red and mottled marls, with beds of gypsum and rock-salt. In some places where sandstones appear they contain numerous plants (Equisctum colunmarc, Truiioptcr-'13s rittuta, I’tcropli_I/Zlmn, &c.), and labyrinthodont and ﬁsh remains. 300 to 1000 feet. Lower (Lettcnkohle, Kohlenkeuper).—Grcy sandstones and dark niarls and clays, with abundant plants, sometimes forming thin seams of an earthy hardly workable coal (Lettcnkolilc). The plants include, besides those above mentioned, the conifers A mucm'o.7cyIon Th in-hzgicum, V oltzia Iwtcroplzylla, &c. Some of the shales are crowded with small ostracod cr1istacea(E.s-tlwria minuta). Remains of ﬁsh (Ccratorlus) and of the Jllastoclonsd-urns Jccgcri have been L obtained. About 230 feet. r Upper Limcstonc in thick beds with argillaceous partings.—It abounds in organic remains among which Ccratitcs nodosus, Nautilus bi(lo7'saf.us, Lima striata, ]ll_i/oplioria rulgaris, Tri- gonorlus S(mdbc7'gcri, Tcrcbratula 'cuIgarz's, and Encrivius liIL'zfor7mIs are specially characteristic. It is a thoroughly marine formation, sometimes almost wholly made up of erinoid stems. 200 to 400 feet. 4 Middle Limestone and Anliydritc, consisting of dolouiites with anhydritc, gypsum, and rock-salt. Nearly devoid of organic remains, though bones and teeth of saurians have been found. 200 to 400 feet. Lower Limestone, consisting of limcstones and dolomites, but on the whole poor in fossils, save in the limestone bands, some of which are full of Tcrebratula vitlgaris and Encrinus _ lilizfomnis. 160 to 500 feet. ( Upper (Ri3th).—Red and green marls, with gypsum in the lower part. 250 to 300 feet. Middle.—Coarsc-grained sandstones, sometimes incoherent, with wayboards of Estlieria shale. Lower.—Fine reddish argillaceous sandstone, often micaeeous and ﬁssile, with occasional interstratiﬁcations of dolomite and of the marly oolitie limestone eallec “ Rogenstein.” 4 The Buntcr division is usually barren of organic remains. The plants already known include Equisctum arenaccmn, one or two ferns, and a few conifers (Albertia and Volt:z'u). The lamellibranch 11[_1/ophoria costata is found in the upper division all over Germany. Numerous footprints occur on the sandstones, and the bones of labyrinthodonts as well as L of ﬁsh have been obtained. Kcupcr. J. M uselielkalk. Buntcr. The Trias attains an enormous development in the eastern Alps, where it bears evidence of having been accumulated under very different conditions from those of the Trias in Germany. The great thickness of its limcstones, and their unequivocally marine organisms, show that it must have accumulated in opener water, which remained clear and comparatively free from inroads of sandy and muddy sediment. It possesses, moreover, a high interest_ as being a massive formation of marine origin formed between Permian X.—45