Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/355

Rh DEVONI.-VN’.] marks that it is singular that the British Lower Devonian rocks should only have yielded 1 gasteropod (I’leurotoma'ria (I-RpL’)'((->, 4 lamellibranchs, 1 ceplralopod (Ort/wceras gracilc), and 1 mrcleobranch (Belle?-ophon bisulcatus). They have furnished only 10 brachiopods. Traces of ﬁsh remains have been obtained among them in the form of bones and copro- litic debris. So far as observation has gone not a single Silurian species has been certainly detected in the Devonian rocks of Britain, with, according to Mr Etheridge, the sole exception of the long—lived and universally diffused Ah-_z/pa wliculcu-is, which occurs in the Ilfracombe group. There can be no doubt, however, from the meagre list of fossils from the Lower Devonian rocks of Devon and Cornwall, that either the conditions for the existence or those for the fnssilization of the early Devonian fauna must have been singularly unfavourable in the south—west of England. It would be exceedingly rash to argue as to the extinction of the Silurian fauna from the unsatisfactory evidence of these rocks. .’l[z'¢I«Ilc.——As above remarked, this is the great storehouse of Devonian fossils in the south—west of England. In this fauna, as tabulated by Mr Etheridge, there are 8 amorpho- zo.1ns, including 5 species of Stromatopora ; 23 genera and 50 species of coalenterates, arnnng which the corals i»lceruularia, Alucolitcs, C'_(,/at/Lop/z_2,/llum, Fuvositcs, Pleura- ¢I£cz‘_z/zun, and I’et7'aia are conspicuous; 4 genera and 8 species of crinoids (I[e.mcri7zus, C’;/at/Locrinus, &c.); 1 annelide (Tenlaculilcs annulatus) ; 5 genera and 13 species of crustaceans, which are all trilobites (I’Iuzcops grcmulalus, 1’. latt'1"rons, I’. pzmctat-us, Brontcus ﬂabcllzfer, C/zeirurus arliculatus, I[a7j7c’s macroceplmlus, &c.); and 12 species of polyzoans. The brachiopods are abundant; 68 species GEOLOGY have been yielded by the rocks of South I)evon, including A!/23/ris concentrica, A. lac/z7'_2/ma, Atrg/pa 1'eticularis, A. dcsvlucunata, Cmmzrop7Lo7'ia 7'/zomboiclca, C'_2/rtina Lemarlii, (lrthis striatula, It’/z_2/no/zonella acuminala, In’. pugnzzs_. Pcntmnerus brcvirostris, Spz'r{r'er disjzmctus, Stringoccp/zalus Jfurlini, Uncitcs gr_1/p/ms, &c. The lamellibranchs are poorly represented, 11 genera only occurring, and many of them represented by only 1 species. The gasteropods are likewise present in but small numbers and variety; 12 genera. and 36 species have been enumerated. Of these species, 4 (.-lcroculia vetusta, Euomplralus lccvis, .Zl[acro- c/Leilus irnbricalzcs, and Jllurc/Lisonia spinosa) survived into the Carboniferous period. The cephalopods are repre- sented by 5 genera, the most abundant speciﬁcally being C_2/rfoceras and Orthoceras; Goniatites, Cl;/mem'a, and .''¢mtilu.s also occur. Of the total list of fossils a large proportion is found in the Middle Devonian rocks of the continent of Europe. Very few species agree with those of the Silurian or with those of the Carboniferous system. Upper.—From the calcareous portions of the Pether- win and Pilton beds of Cornwall and Devon a considerable number of fossils has been obtained. Among the more characteristic of these we ﬁnd 11 species of the coiled cephalopod C'l_ymem'a ((7. undulata, C’. lcevigata, C’. striata), the trilobites /’/zacops granulatus and P. latzfrons, the small ostracod C'_z/1n'idina se7'rc1to-sfriata, the brachiopods .5’/2i2'z_7f'e)' clisjzuzcl us or l'erncullii, .Stro[»/umzcrza rhomboidalis, C/wnetes Ilanlrcnsis, Productus sulzaculcatus, and the lamellibranch Cuculcea Ilardingii. The Marwood and Baggy Point beds have also yielded traces of land plants, such as Ir'no7'ria dic/wtoma and Adicuztitcs I/ibernicus, the latter‘ fern being common in some parts of the Upper Old ted Sandstone of Ireland. The higher red and yellow sandy portions of the Upper Devonian rocks shade up insensibly at Barnstaple in North Devon into strata which by their fossils are placed at the base of the Carboniferous Limestone series. But in no other , series save the south—western district of Britain can such a ‘ 341 passage be observed. In all other places the Carboniferous system, where its true base can be seen, passes down into the red sandy and marly strata of the Upper Old Red Sandstone without marine fossils. CONTINENTAL EUaoPE.—Devonian rocks occupy a large area in the centre of Europe, extending from the Ardennes through the south of Belgium across Rhenish Prussia to Darmstadt. They are best known from the picturesque gorges which have been cut through them by the Rhine below Bingen and by the Moselle below Treves. They have been arranged into the following groups in the Eifel region, where their true geological position was first indicated by Sedgwick and Murchison. III. Upper I)cvom'mr— (c) Cypridina shales (Cypridina serrate-st1'z'ata). (I2) Goniatite shales (/Jorriatitcs rctrorsus, G. primordialis, Orthoccras sub_ﬂe.ruosum, Cardiola 'retr0striata, &c.). (a) Nodular‘ crumbling limestone (Kramenzelkalk), dolomitic marl, and shaly limestone (Spz'r{fcr dzlgiurzctus or Verneuill-i, Atrypa reticularis, Rhymshmwlla cuboides, Productus sub- uculeatus, 620.). II. Jlliddlc Dcvonian— (b) Stringocephalus group, consisting of the great Eifel lime- stone with underlying crinoidal beds (.S'tr1Tngocrphalus Bur- tini, .S'_p2'1'z:fer mzdatus, Productus subaculeatus, Pa-ntamerus galeatus, Atrypa reticztlaris, Calccola sandalina, and many corals and crinoids). (a) Caleeola group,—marly lirnestoncs full of Calccola samlalimr, .S'pirzfcr concentricus, C'amm'ophoria 'nu'cro1'hyncha, &c., resting upon impure shaly ferruginous limestone and grey- wacke, marked by an abundance of .S'pz'7'z_'fcr cultrzjugatus, Rhynchonclla Orbignyana Atrypa rcticularis, Phacops lati- frons, &c. I. Lower 1)eronz'an— (c) Upper greywacke and shale (Vichter-Schichten), with a mixture of Lower and Middle Devonian fossils. (b) Ahr‘ group,—gr‘eyvackc-shales with Clzonetcs sarcinulata, C. dilatata, Rhynchonclla Liron1'ca, .Sj)z'7'1_'fcr pm'ac7o.u(.9, S. syrcciosus, many species of I’tc'rinca, Plr-urotomm'ia, and 1l1urch.z'som'a. (a) Coblentz group, greywacke and clay-slate (Leptaena laticosta, Uhonctcs sarcinulatav, Plzynchonclla Lir0nz'ca, Plcwrod-z'ctyum. problemat2'cum, &c.). This threefold subdivision, with a central mass of calcareous strata, is traceable westwards through Belgium (where the Calcairc de Givet represents the Stringocephalus limestone of the Eifel) and eastwards into the Harz. The rocks reappear with local petro- graphicalmodiﬁcations, but with a remarkable persistence of general palreontological characters, in Eastern Thuringia, Franconia, Sax- ony, Silesia, the north of Moravia, and East Galicia. Devonian rocks have been detected among the crumpled rocks of the Styrian Alps by means of the evidence of abundant corals, clymenias, gasteropods, lamellibranchs, and other organic remains. Perhaps in other tracts of the Alps, as well as in the Carpathian range, similar shales, limestones, and dolornites, though as yet unfossili- ferous, but containing orcs of silver, lead, mercury, zinc, cobalt, and other metals, may be referable to the Devonian system. In the centre of Europe, therefore, the Devonian rocks consist of a vast thickness of dark—grey sandy and shaly rocks, with occasional seams of limestone, and in particular with one thick central cal- careous zone. These rocks are characterized in the lower zones by numerous broad-winged spirifers and by peculiar‘ trilobites (Plmcops, Homalonotus, &c.), which, though generically like those of the Silurian system, are speciﬁcally distinct. The central calcareous zone abounds in corals and crinoids as well as in numer- ous brachiopods. In the highest bands a profusion of coiled cephalopods (Clymemkz) occurs in some of the limestones, while the shales are crowded with a small but characteristic ostracod crusta- cean (C'yp7'id-z'na). Ilerc and there traces of ﬁshes have been found, more especially in the Eifel, but seldom in such a state of preservation as to warrant their being assigned to any deﬁnite place in the zoological scale. More recently, however, E. Beyrich has described from Gerolstein in the Eifel an undoubted species of Ptcriblztlzys, which, as it cannot be certainly identiﬁed with any known form, he names P. I.’hcna7Lus. A Coccostcus has been described by F. A. Roemer from the Harz, and more recently one has been cited from Bicken near Herborn by V. Koenen; but, as Beyrich points out, there may be some doubt as to whether the latter is not a Ptcrz'chtl2g/3.1 A Ctcnacanthus, seemingly urrdist1n- guishable from the 0. Bohcnricrls of Bar'rande’s tage G, has also been obtained from the Lower Devonian “ l'ereitensclri(-hten” of 1 Zeitschrzﬂ der Deulsch. Geol. G'csell., xxix. 751.