. Catalogue of the Mesozoic plants in the Department of geology, British museum (Natural history) [Part III-IV] The Jurassic flora. Paleobotany; Paleobotany. 67 seen in Text-fig. 7 formed along the radial walls of the tracheids; the rest of the section presents the same spotted appearance as that which characterises the yellow matrix of pure jet. The cavities of the tracheids become filled with an orange-coloured substance, and the outlines of their walls may be faintly traced in a micro- photograph of a section of ordinary jet. The contorted appearance of the dark lines shown in a transverse
. Catalogue of the Mesozoic plants in the Department of geology, British museum (Natural history) [Part III-IV] The Jurassic flora. Paleobotany; Paleobotany. 67 seen in Text-fig. 7 formed along the radial walls of the tracheids; the rest of the section presents the same spotted appearance as that which characterises the yellow matrix of pure jet. The cavities of the tracheids become filled with an orange-coloured substance, and the outlines of their walls may be faintly traced in a micro- photograph of a section of ordinary jet. The contorted appearance of the dark lines shown in a transverse section of jet points to contraction of the wood during its con- version into jet. I have no hesitation, then, in describing the dark lines seen in Figs. 5 and 7, PI. VIII. as having been formed by the production of a deep brown substance along the course of the radial walls of the tracheids, their wavy or zigzag form being due to. Fig. 5.—Jet partially enclosing a core of stone consisting of an imperfectly preserved cast of a piece of wood. ("Whitby Museum.) contraction. The mottled appearance of the lighter - coloured matrix is due to the persistence of faint traces or ' ghosts' of the membranes of wood-elements. The flattened form of the large blocks of jet met with in the jet-rock is no doubt very largely due to the compression of the wood in the process of its alteration into jet. It has been pointed out by more than one writer that specimens are not uncommon in which a thin layer of jet forms a crust over a core of stone. In specimens of this kind the thickneas is considerably greater than in pieces of ordinary jet. Text-fig. 5 represents a diagrammatic sketch of an end-view of a specimen in the Whitby Museum, which consists for the most. 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 British M
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