Report on the scientific results of the voyage of during the years 1873-76 : under the command of Captain George SNares, , Captain Frank Turle Thomson, . n-taining lapilli, which are identical in structure and mineralogical constitution with thebasalt of Greenland Harbour. Fragments of phonolite are also seen, and sometimesvitreous lapilli altered into palagonite. Amongst the fragments of minerals in thistufa, olivine, augite, triclinic felspars, and large broken crystals of sanidine may beseen. Some of these, especially the plagic-clases, are entirely penetra
Report on the scientific results of the voyage of during the years 1873-76 : under the command of Captain George SNares, , Captain Frank Turle Thomson, . n-taining lapilli, which are identical in structure and mineralogical constitution with thebasalt of Greenland Harbour. Fragments of phonolite are also seen, and sometimesvitreous lapilli altered into palagonite. Amongst the fragments of minerals in thistufa, olivine, augite, triclinic felspars, and large broken crystals of sanidine may beseen. Some of these, especially the plagic-clases, are entirely penetrated by silica,which has converted them into pseudo-morphs. A group of triclinic felspars ishere figured (fig. 25), which shows thatthey are replaced in the upper part byopal, in the lower by chalcedony. Themass uniting the clastic elements of thistufa seems to be of a vitreous nature, butits characters are vague, and veiled by in-numerable opaque grains, most probably of magnetite, which are scattered throughoutthe substance. The phonolite part of this specimen which is joined to the basalt doesnot present, from the point of view of micro-structure, anything to distinguish it from. FlG. 25.—Basalt in contact with phonolite fromGreenland Harbour. Group of plagioclase epigeuised into opal on the upper part,transformed into chalcedony on the lower. 5*5 crossed light. 136 THE VOYAGE OF CHALLENGER. the normal phonolites already described, except, perhaps, that the sections of sanidineare somewhat larger. Another hill situated at this part of Greenland Harbour is formed of a trachyticrock. It is a rounded eminence crowned by a mass of angular blocks, scattered aboutlike the ruins of masonry. The rocks collected here by Mr. Buchanan are augitictrachytes, identically similar to those already described; they were obtained from thebed of a river entering Eoyal Sound. The rocks are compact, with a slightly greasylustre, and a subconchoidal fracture. They are blui
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectscientificexpedition
