. Le journal trimestriel de la Société géologique de Londres. bail sur les sphérules, avec un pronouncedradial structure et montrant l'habituelle croix noire avec crossednicols. La doublure à l'intérieur de la frontière est fibreux entourant la bande de silice athin claire, puis une couche de la petite, brown, il y a, bien sûr, la possibilité que, dans certains cas, ces fissures sont theresult de contraction en raison de la cristallisation de la matière fibreuse. 460 PROF. S. W. SUR LE EOTJLTON [17 nov. 1904 spherulitic, organes, même si ces derniers sont parfois disposés inbunches- rayonnant à partir de la paroi de l'amygdale towa

• Contributeur: The Reading Room / Alamy Banque D'Images
• ID de l’image: 2AFJ4C7
• Taille du fichier: 7,1 MB (276,1 KB Téléchargement compressé)
• Autorisations: Modèle - non | Propriété - non
• Dimensions: 1919 x 1302 px | 32,5 x 22 cm | 12,8 x 8,7 inches | 150dpi

Informations supplémentaires

Cette image appartient au domaine public, ce qui signifie que le droit d’auteur a expiré ou que le titulaire du droit d’auteur a renoncé à ses droits. Les frais facturés par Alamy couvrent l’accès à la copie haute résolution de l’image.

Cette image peut avoir des imperfections car il s’agit d’une image historique ou de reportage.

. The Quarterly journal of the Geological Society of London. rown spherules, with a pronouncedradial structure and showing the usual black cross with crossednicols. Lining the inside of the surrounding fibrous border is athin band of clear silica, and then a layer of the small, brown, There is, of course, the possibility that, in some cases, such cracks are theresult of contraction due to the crystallization of the fibrous material. 460 PROF. W. S. EOTJLTON ON THE [Nov. 1904, spherulitic bodies, while these latter are sometimes arranged inbunches radiating- from the wall of the amygdaloid towards itscentre. It is clear that the brecciation of the wall of the noduleoccurred before the infilling of this silica and brown spheruliticmatter, for they are arranged in concentric borders around theangular and isolated fragments of the wall. Fig. 1 is a sketch of a nodule 7 inches across, collected by myselffrom locality (433). There appear to be three generations, as it were, Fig. 1.—/Sketch of a nodule of complex structure, measuring 7 inches across.. A—Fibrous border. B=Quartz-amygdaloid. C=Quartz and brown spherulites. in the formation of this nodule. Fibrous borders have been formedapparently around two small vesicles; one nodule thus formed, containing a more or less rounded amygdaloid, has become partlyenveloped by a larger, including an irregularly-stellate quartz-amygdaloid, while all three have been enveloped in a dark-brownfibrous layer, which forms the outer wall of the nodule. A specimen of slag given to me some years ago by Mr. H. T. Walleris interesting in this connection, and seems to have some bearingupon the origin of these pyromeridal and lithophysal structures. Itis a compound vesicle or lithophyse, 1% inches across, in a bluish-grey glassy slag (fig. 2, p. 461). The main vesicle is surrounded byroughly-concentric arcs of light-brown transparent glass, and be-tween these glassy layers are crescentiform spaces. If this structureoccurred in a rhyolite, if

Recherche dans la banque de photos par tags

• bookcentury1800
• bookdecade1840
• booksubjectgeology
• bookyear1845