Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison.

  • Murchison, Roderick Impey, Sir, 1792-1871.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison. Source: Wellcome Collection.

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    clearly recognizable through their position and organic remains, it is not pretended that a line can everywhere be precisely drawn, upon a map, between them and the Caradoc formation; and thus on the accompanying Map the tint 2^ is shaded off into the colour of 2^. In all such cases of junction and passage, the general term ‘ Lower Silurian ’ can alone be with safety applied. Graptolites.—In terminating this sketch of the Llandeilo formation, a few words may be offered on the fossils called Graptolites, already partially adverted to, and which, wherever they are found, clearly mark the rock •to be Silurian. They occur, indeed, in North and South America, Britain, Scandinavia, Germany, Russia, France, and Spain. Abounding in the lowest strata of the Llandeilo formation, which graduate downwards into the Lingula-flags, these Graptolites are specially abundant in the very tract of Shropshire (Stiper Stones to Shelve) on which such stress has been laid as affording the best illustration of a large mass of the inferior strata. They prevail, in fact, throughout the Silurian rocks wherever the nature of the sediment has been favourable to their existence,—that is, in schistose argil- Fossils (12). Lower Silurian Graptolites. 1. Eastritest peregrinus, Barrande. 2. GraptoHthus Sedgwickii, Portlock. Jk G. priodon, Bronn (G. Ludensis, Sil. Syst.). 4. Cliinacograptus scalaris, Linn. 4*. Bi- plograpsus folium, Hisinger. 6. D. nodosus, Ilarkness (a doubtful species). 0. D. fo- lium, Hisinger (young specimen). 7. Dicranograptus ramosus, Kail. 8. Didymo- grapsus sextans, Hall, 9. D. Murchisonii, Beck. laceous strata, or the finely levigated muddy bottoms of the primeval seas. They are supposed by many naturalists to have been Zoophytes nearly allied to the living Yirgularia, a creature known only in deep water. Others rather consider these extinct forms to belong to Sertularian Zoo- phytes, or even to PolyzoaJ. Be this as it may, the geologist has observed that they are found eocclusivehj in the Silurian system of life. The whole t See Geinitz (Veratein. Grauw.-Format.) who, much more complex in structure than any here for the sake of uniformity, groups all the Grap- figured. ^lites with a single row of teeth (GraptoHthus, J Mr. Salter argues for this latter view of their Eastrites, &c.) under the name Monograpsus. affinities in the Appendix to the‘Geology of North Some forms have been discovered in Canada Wales,’ Memoirs Geol. Survey, vol. iii. 1866.