124 BÄCKSTRÖM, VESTANÅFÄLTET. 



8 to 10 times larger than in the surrounding ground-mass. At the same tinie the form of 

 tlie accumulations change from the irregular shapes shown in the least altered varieties 

 (Fig. 24) to lenses, parallel with the schistosity, as represented in the Figures 23, 25 and 

 also 29. — Examples of the transforming through contact-metamorphism of large felspars 

 to granular aggregates of polygonal grains have been described by R. Beck * and by 

 Harker and Marr, 2 and in two of the least altered dense fine-grained gneisses, from 

 Axeltorp and from NNW of Näsum church, caréful search gave some evidence of the 

 former connection of the grains of the felspar accumulations. Fig. 26 completed by the 

 drawing Fig. a on p. 62 shows an accumulation, partly granulated, consisting of one large 

 and many small grains of felspar, the 1 ätter possibly derived from the former through 

 granulation. Fig. b shows another example. — If the felspar accumulations were derived 

 from formerly homogeneous, individual large felspars, then these felspars were no doubt 

 the felspar phenocrysts of the quartzr-porphyrite tuff, corresponding to the quartz pheno- 

 crysts, previously mentioned as sometimes preserved, while by analogy the clark accumula- 

 tions would come from the dark phenocrysts of the tuff with their inclusions of iron ore, 

 apatite etc. Another reason for this is given beneath. 



The mica schists intercalatecl in the gneisses" are linked together with them through 

 all gradations. Generally they are rich in quartz and muscovite, and poor in, but seldom 

 free from felspar. One specimen from Blistorp was analysed with these results 



SiO, 



AL0 3 



Fe 2 3 



FeO 



MgO 



CaO 



Na 2 K,0 



H 2 



Sum 



75,39 



12,69 



1,42 



2,06 



0,36 



0,63 



0,71 4,45 



2,14 



99,85 



From the chemical composition, taken with the microscopical evidence, it follows that the 

 intercalated mica schists represent a material, more decomposed by weathering than the 

 tuff material of the gneisses. This material may still have been derived from the tuff, as 

 the mica schists often contain undoubted elements of it, the most prominent of which 

 are large qua.rtzes, which sometimes are well preserved dihexahedrons. In several of these 

 mica schists the large quartzes are more richly present than in the tuffs, and in one in- 

 stance, occurring 1700 meters ENE of Grön hult, the large porphyritic quartzes were accom- 

 panied by felspar-accumulations with the same mode of occurrence and order of size and 

 well defined against the fme-grained groundmass, that here consists essentially of quartz 

 and muscovite (Fig. 28). Evidently, the felspar-accumulations like the quartzes have be- 

 haved as large single grains during the sedimentation, which agrees with the previously 

 expressed opinion, that the felspar-accumulations a,re the felspar phenocrysts of the tuff, 

 afterwards granulated through contact-metamorphism. They were here, together with the 

 quartz phenocrysts, washed out of the tuff and inbedded in material more rich in quartz 

 and muscovite. 



1 »Erläuterungen zur Geologischen Specialkarte von Sachsen, Section Pirna» p. 36 (Leipzig 1892) and 

 Min. Petr. Mitt. 13 p. 326 (1893). 



2 Quarterly Journ. Geol. Soc. 48. (1891) p. 296 and 300 (Given literally in this paper p. 61—62.) 



3 Represented with the same colour as the cpuartzite on the map. 



