File:The Quarterly journal of the Geological Society of London (1881) (14767539971).jpg

Identifier: quarterlyjourna371881geol (find matches)
Title: The Quarterly journal of the Geological Society of London
Year: 1845 (1840s)
Authors: Geological Society of London
Subjects: Geology
Publisher: London (etc.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ss;evidently a crystalline coating had been dissolved away from them;and in the slender siliceous rods which remained one recognized atonce true sponge-spicules. The sediment was next examined. It contained a number of largesiliceous spicules, some of which are figured on page 255, also somesmall colourless transparen t hexagonal prisms capped with six-sidedpyramids at each end, evidently quartz crystals, and, finally, someminute rhombohedra, which were subsequently found to be mag-nesite. The Sjjonge-Sjncules.—By reflected light the spicules appear snow-white, with a vitreous lustre; by transmitted light they are glassy andtranslucent; when immersed in water, glycerine-jelly, or Canada-balsam, they become quite transparent, except in places where theyare traversed by a minute black spongy network which appearswhite and shining with reflected light, and. evidently contains air:when this is displaced by the liquid medium, the spicule becomes FEOM THE SILFBIAN EOEMATION OF CANADA. 255
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256 W. J. S0LLAS ON A NEW LYSSAKINE HEXACTINELLID transparent throughout; it is frequently colourless, but sometimespresents a faint yellowish browm tint either in places or throughout.The surface of the spicule has a rough irregular appearance whenexamined dry, which disappears, however, on immersion in balsam,being evidently due to a crystalline incrustation (magnesite). Whenthis is removed the sides of the spicules appear as neat continuouslines; the axial canal is also quite sharply denned, and is sometimesnot more enlarged than in recent deciduous spicules, thoughoccasionally it is so wide as to reduce the spicule to a mere shell. Insome instances it has been infilled with silica, so as to appear as acylindrical rod projecting from what remains of the spicule in whichit was formed (fig. 8, p. 255). The spicules are not excavated by rhombohedral pits like thoseseen in Hyalostelia Smithi, Young, from the Carboniferous Limestoneof Scotland ; but sometimes they are pitted all over wi

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