. Elements of geology. Geology. 268 LYELL'S ELEMENTS OF GEOLOGY. Lower Silurian Rocks, and their Fossils. divisible into similar groups. They are composed of large de- posits of sandstone, which is sometimes found at the base of the system, resting on gneiss and calcareous rocks, with orthocerata and corals ; the chain-coral, (Fig. 278.) before mentioned, being very conspicuous 5 also fine bituminous shales containing grap- tolites. (Fig. 280.) These bodies are supposed by Dr. Beck, of Copenhagen, to be fossil zoophytes, related to the family of sea-pens, of which the living animals inhabit mu
. Elements of geology. Geology. 268 LYELL'S ELEMENTS OF GEOLOGY. Lower Silurian Rocks, and their Fossils. divisible into similar groups. They are composed of large de- posits of sandstone, which is sometimes found at the base of the system, resting on gneiss and calcareous rocks, with orthocerata and corals ; the chain-coral, (Fig. 278.) before mentioned, being very conspicuous 5 also fine bituminous shales containing grap- tolites. (Fig. 280.) These bodies are supposed by Dr. Beck, of Copenhagen, to be fossil zoophytes, related to the family of sea-pens, of which the living animals inhabit mud and slimy sediment. Fig. CraptoUtcs, Linn. a. b. Graptolites from Christiania, Norway, c. rf. Graptolites from the south of Sweden. In the limestones of Lake Michigan, in North America, and other regions bordering the great Canadian lakes, chain-corals and trilobites are also found, and from their fossils generally Ihey seem to belong to the Silurian period. They contain cer- tain orthocerata, which have a very peculiar structure. The siphuncle is very large, and has a tube running through its whole length, from the outside of which radii set off in verticila- tions extending to the inner wall of the syphon, these verticila- tions corresponding in number to the chambers of the shell. Mr. Stokes, who has described this division of orthoceratites, has formed them into a distinct genus, for which he has adopted the Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lyell, Charles, Sir, 1797-1875; Gibbes, Lewis Reeve, 1810-1894, former owner. DSI; Merrill, George P. (George Perkins), 1854-1929, former owner. DSI. Philadelphia : James Kay, Jun. and Brother ; Pittsburgh : C. H. Kay & Co.
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Keywords: ., bookauthorlyellcharlessir17, bookcentury1800, booksubjectgeology
