. Acta Academiae Aboensis. Science; Mathematics. 108 SIERRA DE UMANGO Evidently it is a more acid (trachy-) andesitic ting extinction, rock. Another rock associated herewith, is a reddish brown porphyrite containing pale phenocrysts of feldspar. Microscopically it reveals abundantly potash feldspar as phenocrysts and also as greater frag- ments. The groundmass is composed of a glassy (?) substance with inhomogeneous pigment of iron ore dust. The glassy residual. Fig 15. Lava and tuff accumulations (dark fiills in the background) of probably tertiary age, seen from the eastern wall of the Tambi
. Acta Academiae Aboensis. Science; Mathematics. 108 SIERRA DE UMANGO Evidently it is a more acid (trachy-) andesitic ting extinction, rock. Another rock associated herewith, is a reddish brown porphyrite containing pale phenocrysts of feldspar. Microscopically it reveals abundantly potash feldspar as phenocrysts and also as greater frag- ments. The groundmass is composed of a glassy (?) substance with inhomogeneous pigment of iron ore dust. The glassy residual. Fig 15. Lava and tuff accumulations (dark fiills in the background) of probably tertiary age, seen from the eastern wall of the Tambillos valley. Looking north. The domeshaped summit in the dis- tance is the Cerro Cacho. The promontory in the foreground is of the old crystalline basement. The even slope is sheet flood gravels. mass contains occasionally cavities. There are also smaller frag- ments of quartz and the rock may be classified as a quartziferous syenitic vitrophyre. Intercalated between these lava masses lie tuff layers, gene- rally of paler colour and well visible at a greater distance (cf. fig. 15). These layers dip all northward. Microscopically, the tuff contains abundantly grains of corroded quartz in an allotriomorphic mass of pigmented feldspar and small quartz grains, irregularly distributed. Another specimen of the tuffs shows a high degree. 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 Åbo akademi (1918- ). Åbo : Åbo akademi
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectm, booksubjectscience
