Proceedings of the United States National Museum . 025 2016 1130 1730 0329 5610 16 63 03 75 33 76 3080 5256 1644 3266 1060 1063 3778 2166 0626 2271 48 o / 30 0030 0030 0030 0030 0030 0000N. 0630 0030 0030 0010 53 63 07 23 P. dull Med 75 4775 47 4 p. dull 80 24 5 P. blurred .. 55 57 6 Med 44 36 7 P. 66 18 8 P N. c. 9 P. blurred *. 63 48 10 Medium 78 32 11 V. p 65 45 1? Medium . 26 15 13 Good 69 02 A later deposit of calcite occurs as a minutely drusy botryoidalcrust. This varies from a continuous crust which may envelopelarge crystals of the last described form, to minute spherica
Proceedings of the United States National Museum . 025 2016 1130 1730 0329 5610 16 63 03 75 33 76 3080 5256 1644 3266 1060 1063 3778 2166 0626 2271 48 o / 30 0030 0030 0030 0030 0030 0000N. 0630 0030 0030 0010 53 63 07 23 P. dull Med 75 4775 47 4 p. dull 80 24 5 P. blurred .. 55 57 6 Med 44 36 7 P. 66 18 8 P N. c. 9 P. blurred *. 63 48 10 Medium 78 32 11 V. p 65 45 1? Medium . 26 15 13 Good 69 02 A later deposit of calcite occurs as a minutely drusy botryoidalcrust. This varies from a continuous crust which may envelopelarge crystals of the last described form, to minute spherical glob-ules, and ranges in color from white through yellowish to smokygray. The surface of this crust is made up of minute curved flatrhombohedral crystals. This deposit of calcite was formed after theremoval of the anhydrite and occurs in places in the anhydritecavities. 30 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 68 Chalcedony was found in megascopic masses only once as a pur-plish-gray filling of a cavity lined with calcite crystals. Its micro-. FiG. 8.—Calcitb. Habit of largee colorless crystals scopic occurence in lime-silicate rock has been noted above. Thechalcedony is in the white earliest calcite in the calcite veinlet above ART. :.8 MINERALOGY OF TEIASSIC LIMESTONE SHANNON 31 the basalt dikes as described above. It forms an irregular mass15 millimeters in maximum diameter, varying from chalky whiteat the borders to translucent purplish gray in the center. It hasthe usual lusterless surface and flinty fracture. EXPLANATIONS OF PLATES Plate 1 Replacement of limestone conglomerate along a narrow fissure. Shows thereplacement of the calcareous sand forming the matrix of the pebbles by amixture of diopside vesuvianite and garnet and, nearer the fissure, later re-placement by magnetite. Two-thirds natural size. PlATE 2 Crust of datolite crystals encrusting the walls of a narrow open fissure inlimestone. Natural size. Plate 3 Upper left: Rectangular mold of anhydrite crysta
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
